Something that used to annoy me when I started out making things out of leather was the tendency for a little gap to appear at the intersection where multiple seams came together. It was like a little hole, and it really bothered me, until I came up with a little fix. Here's a little drawing showing the problem: See the little black triangle? Unacceptable!If you flip the workpiece over, you'll see the 2 panels on top meeting the third panel below, with their seam allowances folded down and topstitched. Part of the issue is that leather is not completely flat - it has a thickness. And when you fold that thick material, you are creating a little bit of space because it is impossible for the fold to lay completely flat. It seems to compound the problem when you have 3 or sometimes 4 panels coming together in one place.
Let's back up to see where the problem is. Here we have the same 2 panels as before - sewn together, but not yet joined to the third panel. At this stage I would clip the seam allowance at a 45º angle before clipping and sewing the third piece.
Leaving this kind of shape:
You can get an idea of the problem already. I now have to sew exactly on that seam line to keep the gap from showing up. And, as we know with leather things can stretch and move around while sewing, making precision alignment difficult at best. So my solution was the idea below: Clip one side of the seam allowance in line with the seam. Let the other seam allowance form a tab, which is folded over before sewing.
Once folded over, I usually trim that little flap (see the dotted line below) so it doesn't create too much thickness at the seam. This method has worked really well for me, and the gaps have been officially banished - even with 4 panels coming together - it's been a simple and effective solution.