No such thing as a stupid question! On stemmies, trim away all you want, as all nodes have the potential to put out new roots. On others, I always trim some, because it's easier to leave some roots to help in the anchoring of the plant once you plant it.
Trimming will remove damaged roots and also encourages new root growth on the rooted plants like swords and crypts. It also makes it much easier to replant as some of the roots I've pulled up have been 8+" long. For a small plant I'll leave about 2" long roots, larger plants I leave longer roots.