I'm with FF46. I cut as I go. To me, pre-cutting could possibly lead to a mess, especially in a drafty room. I think it's best to handle fur or feather only once while tying a jig.

Of the hair, I believe that I've read about synthetic craft fur being a pain to some tyers due to the short hair mix among the longer fibers. This situation can, at times, lead to a very bulky body with cowlicks behind the jig collar if the short fibers aren't removed. Removal is an extra step.