I work with a lot of leather, usually 6-7 oz, but also from 1oz up to 10-12 & various types (though don’t put chrome tanned in the GF).
As others noted, leather chars when cut or etched. The laser is burning organic material–it also chars wood and paper, though often with those the soot blows off, but it “sticks” to the leather. And so I most often still hand cut as faster than cleaning the edges, but some of my designs I do like to cut, though often have to finish the cut by hand. And I always wash the soot off the edges or any etchings–don’t want my customers to get soot on their fingers!
Variation for cutting with a laser is not just due to the thickness with leather. It’s a skin, and different animals and different areas of the hide have different properties & densities. The back, shoulder & butt will be thicker & tougher than the belly. So what works great with one piece may not work as well with a piece taken from a different area of the same hide!
Also if there’s a scar in the skin, this is a dense area, even though you may not see it, it may cause a localized spot to not cut as deeply.
Also how it’s been tanned will affect cutting–some leathers have more oils and “stuffing”, though that is minimal with natural veg tan… And all leathers are split to desired thickness, but some are also pressed to final thickness, and this can also cause additional variation within the hide…
All in all, leather is great to work with, but expect to have to do some hand trim to finish the cut, and to clean the soot off the edges or any etched areas, so allow extra time for that. (I like bit of mild soap & water with soft toothbrush & get excess water off, and let leather air dry–laying flat or take the opportunity if thoroughly wet to mold it).