My understanding, maybe incorrect, is that when the glowforge head moves to the center of the part and the red laser comes on briefly, the machine is verifying the height of the material compared to what you may have entered.
If this is true, and if you have a part that is not a consistent height, will this throw off the cut? For example, in my photo mat project, I am cutting out the openings for the pictures, removing my masking, and then going back a second time and engraving the captions. So it’s possible that when the machine gets ready to begin the engraving step, it will take its “check measurement” where there is a void in the part. Will this have any effect on the final outcome, if i have already specified the material thickness and focus height when setting up the job?