I'm a longarmer -- I'm working on a quilt right now with 3 seams in the back. The owner did not cut off the selvege and did 1/4" seams. The seams pulls as they say AND the seams will not stay flat. It causes "bumps" along the quilt and I have trouble keeping the machine on the straight and narrow. So -- save yourself and your longarmer a lotta grief and cut those babies off and do 1/2" seams -- and press the seams OPEN!
on edit: To explain --- I pressed the seams open before putting it on the machine --- but 1/4" seams do not seem to want to stay open. :) And I used starch, too!!!