Based on the advice I've gotten:
PDs hire people to do a chronically stressful job. Stress is a risk factor for relapse. Relapse means acute illness for you and burdening others in the programme, distracting them from doing their jobs (a job that entails learning, taking care of patients, developing professionally, etc.). It's a question of fairness, fairness to yourself and fairness to others.
If you came to a PD with a very clear understanding of your disease (or life situation), demonstrated situations where you've endured chronic stress successfully (like acing your Step 1, clinicals, etc.), presented a proactive management plan, said you would save up vacation time, etc, then that's very different.
But if you were vague or deceptive and then had a depressive episode with none of the above, you would have been very, very unfair to everybody, including yourself.
Psychiatrists know how bad things can get, especially if somebody who appears to be clueless about the risk of and implications for relapse rushes into a chronically stressful job. Why would they facilitate that? Is it discrimination? Yes. But that's the situation.
PDs aren't unreasonable people. And maybe a residency with 80-hour/week PGY-1 rotations and ICU terms isn't for you. But whatever you do, just don't be vague. Don't let their imaginations wander, because they've seen the worst, and the worst can be really bad.
You're a med student repeating hearsay. You don't really know how this works until you're on the other side.
That's unfortunate. Do these psychiatrists not believe their patients can make meaningful and lasting recoveries? Or is it more that even a small possibility of relapse is too great a risk for the program considering the number of viable applicants presumed to lack that vulnerability? What advice would you have for someone who did take a medical leave due to a mental illness, if their step score and academic career thereafter was strong/unconcerning? How should they package themselves to address PD concerns without oversharing? An authority at my school told me to explain that I took time off to take care of my family. When I said that felt somewhat disingenuous, he said: "well, you're part of your family."
Edit: Though OP is an IMG, I'm an American student from a middle-of-the-pack allopathic school.
Psychiatrists do hope and know that their patients can get better, but at the same time a PD does NOT want to be down a resident for reasons I already mentioned above. Also, doctors (especially in academia) tend to look down on.even patronize their patients, and while a psychiatrist might praise a bad bipolar or alcoholic for achieving stability in life, working, having a family, they almost certainly do not want that patient doing the same job. So given a large number of applicants for very few spots, it becomes very easy for a PD to skip over/not interview/not rank highly an applicant with a past history of mental illness.
In terms of disclosure, there is not a clear cut answer. Generally, however, in the appropriate section of ERAS putting "had to leave for medical reasons" (ie, being vague) is the way to go. Doing this (ie, being vague) will more likely than not cause the PD or whoever is reading your app to gloss over this (assuming no other red flags) and focus on other parts of your application. However, if you had red flags (behavioral problems that appear in the MPSE, academic problems) due to your illness, then it might require some more disclosure.
Also, you have to consider that your history might delay you from getting a license on time to start July 1 (or mid June). The level of detail asked about mental health/substance issues varies among the different states' applications (most are inappropriately intrusive, unfortunately). If you are monitored under a state Physician Health Program (most of these monitor doctors with only addiction problems, but some do other mental health issues at well) and you match in a state that likewise has a mental health PHP, this can help expedite the process. While starting later in intern year isn't THAT big of a deal (happens to lots of IMGs), letting a potential PD know who might otherwise have no qualms about ranking you is going to be a big judgment call on your part. If you wait until after match day to bring this up with your PD, he or she *might* be a little irritated, but again, you have to balance this with having as many options on the table as possible.
Regarding your personal statement, these types of statements are NOT unique or uncommon, and a large percentage appear to be huge rationalizations for academic/behavioral problems in the past, but they come off sounding like complete BS: "I did badly in med school and had to repeat a year, and then I was diagnosed with xyz, and it really inspired me to go into psychiatry". However, if your experience with your issues GENUINELY drove you to choose psychiatry over another field and you can write about it without coming across as sounding indignant, lame, desperate, then it could be an interesting read. The key is it has to be genuine, so know yourself. Anyway, personal statements don't matter that much (nowhere near Step 1 score, where you went to med school, or clerkship performance).
I hardly see the value in saying "taking time off for family reasons" That is totally disingenuous.