I am aware of the obvious when using brad nail guns or even finish nail guns
for molding, cabinets, furniture and other completed assembly. Is there ever
a time to use a finish nailer for a constructed job such as door frames or
other projects when using wood/boards less than a 2x4 thickness?

For example, I am installing a door and frame to a room in my basement. I
need to attach a header and side supports to fit the frame. To fill in the
difference will require 1x6 on each side, which to me, seems a bit thin for
a framing nailer. Therefore I'm thinking of using the finish nailer.
Basically, is there a general rule perhaps based on the wood used, when to
use a finish and frame nailer?

Thanks