Well for job interviews you always send a thank you letter. Though these days it's more likely to be a thank you email. In that realm, it's seen as good to put your name out there again, show enthusiasm for the job, etc. And it's never a bad thing to show good manners. But that's also in the situation where they give you a business card to contact them if you have any further questions, and they're not likely to be interviewing 200 candidates. Maybe they're interviewing one person at a time, or at most a handful of candidates.
I'd think that in this case, they probably don't want 200 thank you emails. But if you feel like you had a really nice personal connection with someone or it was a more than 20 minute interview, maybe it makes sense? I probably side with the idea of do what feels right to you following the interview.