do you need to put finish on under wraps?

Nope...

do you need to put finish on under wraps?

You dont have to but I like to.......makes for an easier over wrap.

do you need to put finish on under wraps?

You don't have to finish and underwrap. It does make it easier but adds time to the process. I never finish underwraps unless I'm trying to put an small thread (e.g., A) over a large thread (e.g., D). The problem there is the A falls into the D gaps. Still, I just do a back wrap to cover the gaps.