I think the "left adjoint"/"right adjoint" thing is mostly just terminology, although probably now that I've said that someone's going to point me to a n-Cafe post or a SBS where they explain that it's deeply tied to TQFT or something.

I asked a [question][1] a couple weeks back, the answers to which helped me understand why so many functors did have left adjoints.


  [1]: https://mathoverflow.net/questions/5786/how-do-i-check-if-a-functor-has-a-left-right-adjoint