Sewing thick seams can result in skipped stitches, ruining the look of your finished seam or hem. Repairing jeans, or hemming denim is such a time I call out the reinforcement. I use the jean-a-ma-jig.
I have been cutting up old jeans and making skirts, and purses. This tool comes in quite handy. If you don't have one, use a thick piece of cardboard, or a stack of sticky notes. Anything to raise the height of the foot.
First, place the tool behind and under the presser foot. Begin sewing across the seam. After a few stitches, pull it from behind and place it in front. Continue sewing until off the seam.
Bernina, Viking, and other companies special tool for their machines. If you don't have them, try the Jean-a-Ma-Jig, or some raised cardboard, or even the sticky notes. Your seams will not have those skipped stitches.