I applied for - and didn't get - a NHSC scholarship before starting my first year. I agree with what people have said so far, you definitely should be someone who wants to serve in this capacity even if there were no scholarship for doing it. Bottom line, no amount of money is likely to make you happy if you are stuck somewhere you don't want to be. And there do seem to be stiff penalties for those who break their committments to the program.
I applied because: 1) $$$$$$ 2) I enjoy volunteering and serving in places that need it 3) I grew up near underserved rural areas & liked the idea of working in a rural area like one I grew up in 4) I'm interested in primary care 5) I liked that I had some level of control over where I went to work in the end (as opposed to some other service committments).
That's another thing to consider; as a medical student, you would be required to work in an area of 'greatest need'. They have a listing of all these places that have spots for NHSC folks, but as a doc, you would only be able to choose from a much smaller list of places deemed 'greatest need'. Only when those spots get filled, would you be able select a location on the bigger list (not likely).
The NHSC is a gov't program & they aren't just trying to altruistically help medical student debt & temporarily fill healthcare shortages. The goal is to fill these places long-term with people who want to be there (and often have connections to the area). Thus, they are selective. From what I've found, a great great number of students in the program are second & even third-time applicants. Just another way to be sure they're getting someone committed.
You probably have also heard about the 2-year loan forgiveness program that NHSC does as well. The $$$ is capped, so it might not be as good a deal (like if you went to a 40k/yr private school), but it is something to consider if you aren't sure about giving up some of your freedom just yet. You can sign up for it at any point in your career (as far as I know) & your options for locations are not limited to the aforementioned 'short-list'.
There certainly are lots of things to consider & you really need to search your own soul. My take is that service committments are usually only a good option when they fall in line with what you would do anyway & location is no issue.
Good luck