If your compressing something, the best way to look at it, is that you need to know why your doing it. To many people compress things because they've heard its a good thing to do, or someones told them it will help. Its easy to over do it with compression, and you can end up ruining something that was fine in the first place.
A lot of sample packs will have processed hits, and chances are they've been done with good kit. As was said a bit further up, a bit of bus compression can still help, but as for processing each hit, unless theres an obvious need for it, Its probably more hassle than its worth.