I lightly file the edges that will be glued, but dont trim any of the rest of the part. Then I glue it, then sand the seam, and theres no gap to fill. When I used to completely clean up all edges, I would end up with a void. What I mean by cutting off the pins is the locating pins inside of a two half part. Most of the time using the pins will result in a misaligned part. On the fuel tanks, rear ends, air tanks, and parts like that.