Auto increment is a no-no?

Hello. I must confess that I am rather new at this. During my courses, I was taught to place an auto increment as an id field in my tables, when in need to.

However, recently, I heard someone comment that this is to be completely avoided. But I do not understand why. Perhaps anon could point me in the right direction?

>>29
I've only worked on a few databases, but each one gave me the impression that the best primary key is a semantically empty primary key. When you've got to maintain this database for over 10 years, three managers, two application changes, etc., every single decision you make wrt semantics will be invalidated eventually.