I do not trim or straighten edges unless fraying or weird cuts have made a large width on the edge unusable and problematic. When I have weirdly shaped pieces that are big enough to fold, I fold in the wonky edges until they make a regular shape then fold it "properly." I don't have a standard size of strip, unit or block that I regularly work with so, like others have said, I like to keep fabric intact to avoid being 1/4" short for something! :-)