I have never had it result in getting the job, but it has resulted in finding out they had filled it. Many companies don't bother to respond at all to unsuccessful applicants. So perhaps you'll get some closure.

Email right after interview to say thank you. Then no more emails. They are annoying.

Maybe it's just me as a naturally not-pushy person, but I've never done this. I figure the odds are more likely that it'll reflect poorly on you than positively.

No, but I wouldn't hold it against someone either if they did it once. I'm aware career offices at schools give out a lot of bad advice, and I'm not going to fault someone for following common advice. Now if it got excessive, then, yes that would reflect badly on the applicant.

I'm a hiring manager and the "just following up on my interview" email has never led me to hire someone. I have made a quicker decision about someone's candidacy because they followed up letting me know they had another offer (in the particular case I am thinking about, the decision was to tell them to take the other offer), and I have given candidates an update on the state of the timeline when they have followed up.

So if you want an update or have another offer, then sure, follow up. I cannot picture a situation where a follow up email would change the decision, though.