DISCLAIMER: This post is based on my experiences and the experiences of my friends. Different people have different experiences, and I don't want to make the mistake that some do by decreeing that my experiences must be the objective reality of the universe. Your experience may vary.
The real, but not incredibly helpful, reason to apply to any of these programs, a combined program or a fellowship, is because you want to. With the exception of child fellowships and forensic fellowships, they aren't necessarily practical if you want to work outside of major institutions and you want to do reasonably mainstream sorts of work. If you want to develop a specific expertise, fill a niche in a large organization, or want to be involved in academics as an educator, an expert in a particular subfield, or a researcher, then the programs may make sense.
If you're motivated by entirely practical things, that's fine. You probably shouldn't read further. You can if you want.
If you're motivated by other things, like a desire to do a specific type of job for a specific population in a specific setting, want to be in academics, if you want to be an expert in something that your colleagues aren't, then pursuing these unnecessary paths is an entirely reasonable option. They may not be requisite, but they are reasonable.
I know folks who have graduated from 4 triple board programs, 3 family med/psych programs, and 1 IM/psych program. About half of these folks were absolutely miserable during their training, feeling they were spread too thin and unable to concentrate on electives and things they were very interested in. The sort of people who want to do these programs tend to be overachievers, and the idea that you have to be good at everything but maybe not great at anything (at least for the first few years) can be really frustrating. It's hard watching your colleagues in psych working 55 hour weeks as a second year while you're still working 80 hour weeks on inpatient units. It's hard having less elective time because, frankly, your "elective" was picking up the other specialty. Towards the end, these folks would tend to develop some more specific interests, would have more time to pursue them, and seemed happier. In retrospect, pretty much everybody was happy they made the choice they did, even if it was rough getting there.
Most of these folks did not go to these programs because they "couldn't decide". I can't think of any of them who ever said that. Of course, motivations are subject to later revision.
Contrary to what most people here say, most of the folks I know who have done these programs are actually practicing a little bit of both. Most of them are able to do this because they are in large academic settings and have already sacrificed pay and have some flexibility in what they do. The pediatricians see more kids with developmental disabilities, and the adult docs work in clinics specifically designed (even connected with) clinics that service folks with severe and persistent mental illness. This is a unique setting, only available in particular environs, and not something one would broadly count on, but it exists where I am and in places where some friends are. The IM/psych guy did do a c/l fellowship after his residency. Most of his time is spent doing c/l, but he has a day or so a week in the medical clinic for the SPMI population.
I still believe the overall trend is for folks that do combined residencies to wind up mostly practicing one specialty, and that specialty tends to be psychiatry or, in the case of TB programs, child psych. But that's not an absolute.
Regarding the "non-essential" fellowships, they're really a matter of what kind of psychiatrist you want to be. In many settings, even in academics currently, you can still get jobs doing c/l and addiction and geri without fellowships, especially in programs in less desirable areas (outside of VERY major cities--not particularly undesirable areas). Much of this is because the number of folks trained in geriatrics, c/l, and addictions is a small number. Most places cannot require it at this point, and may never. That said, at least where I am, folks with such fellowships will be strongly preferred over another. But many places are just trying to fill a spot and are happy if you speak English, never mind have a specialty training. In larger organizations and in academic organizations, this trend may go towards subspecialization. Whether that matters in 2012 isn't entirely clear, but it's probably fair to say it doesn't matter yet. In 2017? Who knows. Trends are hard to predict.
If you are sympathetic to the idea that "I want to be a specialist in this area, I want to have a whole year devoted to in-depth training and reading and learning about this area, and I can survive one more year with a pgy5-6 salary," then the fellowship may be for you. If you want to be a researcher, it's a slam dunk. If you want to be an academic otherwise, it makes pretty good sense. If you want to do private practice or work outside of large organizations and you don't have to live in a city with a large number of psychiatrists, then maybe it's not for you. Whether you want to do the fellowship or not is all about your goals and what you want. The fellowships tend to support the goals of a minority of residents. That's okay. It's a big tent. Not everybody likes cilantro, either.
The only real cost to doing the fellowships are the opportunity costs. An opportunity to make 100k-ish more that year. The opportunity to take a particular job you want to take that may not be available later. The opportunity to go ahead and get a practice going. Opportunity costs are important. They are also not the end of the world.
Either because they are actually good or because people don't like cognitive dissonance, most folks who do these fellowships are glad that they did them. Maybe it's because they were the sort of people whose priorities the fellowships match, but also because when people spend a year doing something for less pay, there is certainly a tendency to rationalize that in your head. By either mechanism, I don't think many people regret the decision to do these fellowship.
I do get tired of the universal declarations on this board that say that there is no reason to do these fellowships or combined tracks. That's simply untrue. Whether they support your personal and professional goals is another matter.
One last thought is that a particular fellowship at a particular location might not make sense. I'm looking at addiction fellowships, and I've been around the one at my medical school and the one at my residency. Both of them produced very skilled graduates who were more highly in demand, continued to specialize in addictions in academics or in large organizations, and who felt very confident in their ability to handle pretty much anything that came their way. So, I think addiction fellowships make sense. If you haven't been around a very good program, maybe you would come to an opposite conclusion about addiction fellowships. At both of these programs, it would be difficult for a new graduate to be considered for a spot doing addiction psychiatry as an attending without the fellowship. That wasn't true just a few years ago. How generalizable is that now or in the future? Maybe not much.
It's your life. You don't have to be a martyr to please other people and work harder than you have to. You also don't have to feel bad if your particular career goals are different than someone else's and if you are motivated by different things than someone else. It doesn't make you better or worse than them, it just makes you who you are and who you want to be. Okay, now that I'm in full after school special mode, I should stop.
