IMO, this can be an extremely complex & often polarizing subject.
What species are you thinking of, and (captive bred (CB) or wild caught (WC) aside) why would (or do) you want to import one vs. obtaining one without all the hassles & red tape involved in importation?
For species commonly in the pet trade, the only good reason I can think of OTTOMH (and this is just personal opinion) is to introduce or strengthen lines (BICBW).
For more exotic or rare species not normally found in the pet trade, other factors like conservation status may come into play.
I'm from the UK and my only choices are Yemen or red bar panthers, I'm all for a panther but the breeders down here are questionable (ones I've been in contact anyhow) i was hoping to secure a pure CB from breeders who know what there doing.