I trim to the quilt edge while squaring it up. My bindings are always full since the 1/4 inch binding on the front has the binding selvages, quilt top, batt and backing enclosed in them. I try to not trim any of the quilt edge away that will effect the top but I usually have a plain border so a smidge trimmed away doesn't cut any points off. I don't just cut my quilt edges straight but use a large square in each corner with my rulers in between so the whole quilt is squared before doing binding.