For what its worth, I dont use barge or contact cements on my leather work so I shouldnt really say that they are great or a pain either way, but generally I recommend that glues be avoided so you dont have coloring problems later on...Im in the habit of laying out my stitches with a wheel first,then laying the pieces together that are to be stitched, and tacking them at a few places along the edge with a "keeper" stitch to keep every thing lined up and in place...this works quite well for me and the bags I make...the keeper stitch is just simple overhand knotted single stitch, and its removed as the work progresses...
maybe I just learned to work with out it, and so have never felt the need for glue, because others I know have definately had good success with contact cements for some of their work...
TCA