When the glass fibres are saturated with resin they get very slippery and will slide over one another and take on quite convoluted shapes. It helps the distortion if you wet out the glass right to the edge, even beyond the sheer, as any dry glass on the edges will inhibit its ability to take on new shapes.

Good point.
Once I have all the glass on the hull wet out, I quickly trim the excess cloth from the edges, leaving only an inch or two (of wetted glass) hanging. I find that having less excess cloth helps. I did learn through experience that being too 'stingy' about trimming the dry glass before wet out can cause problems as the glass magically moves to uncover part of the wood at the edge when I am not watching!!