where is it important to wrap copper pipe?

Just wondering where it is important for the copper to be wrapped with insulation? Its my understanding that its a must on exterior walls. But ceiling/interior walls its not necessary. \

My concern is condensation on the cold water pipe, but the general info that i've gotten is that hot/humid air is not going to be present inside a finished wall/ceiling.

It is possible that it can. I would insulate all piping, but I wouldn't open up walls to do so.