I sew my trimmings together right away so I don't have to figure out which ones fit together later. But I wait to trim them into a square until I'm putting them in a project, so they are all trimmed to the correct size for that project. I find I am more accurate with flying geese blocks if I start with a rectangle the size of the finished flying geese block and sew on the squares and trim. I don't feel I am wasting the fabric, as I have the part I trim off all sewn for a 1/2 sq. triangle project later. I love scrappy quilts, so this just gets my juices flowing fun projects with scrappy 1/2 sq. triangles.