One way to think about the app process is what things will rule you in vs rule you out of either interviews or getting placed high on the rank list. In my opinion, for example, a board score can rule you in or out. So can research experience. But the personal statement is mostly something that can rule you out (but only rarely). Reasons to be ruled out with it include: misspellings, grammatical errors, not being able to write simple, concise english and sounding like a wierdo. Again this doesn;t happen much, but if you say you keep rodents as pets, or enjoy tasting your petri dishes, people will throw your application in the trash. In perfect world, PS would be used to define who you are, why you are interesting/ different etc. Maybe for family medicine. But for many fields, people want you to sound like a worker who is reliable w/o risk. Err on sounding conservative, and not like a social radical, even if you prefer the latter and perceive yourself as such. Also, its easy to write something thinking you are making one impression, only to actually be making a completely different one. For example, if you talk about how much you love playing chess because of the strategic thinking or basketball because of some reason, keep in mind people may think you just want to play chess or ball, and not get the job done.
Personal statements are a huge source of stress for applicants. This is stupid because they don't matter much. But as some have alluded to, you never know who will read it and care about it. So keep it short, sweet, and make yourslef sound like you will deliver on the tasks demanded of you.