Hey there! I just joined tonight and I've been cutting garment and upholstery leathers with single passes on our Trotec 120W. We have also cut and engraved on oil tanned leather for a steampunk corset. With the 120W I generally cut at 45% power and a relatively fast speed of 3 and frequency of 15000 (not sure how that translates to other machines). Most of my leather cutting has been for a local 'special interest' shop and consists of letters to be appliqued and/or designs to have colored suedes applied behind them.
While the laser DOES brown the edges, most of our clients feel that it adds a finished look to the piece. For Vegtan we mask the surface before cutting, so any smoke deposits will only be on the bottom. We've optimized our venting also, which helps get the smoke away from the material as quickly as we can. I generally use a temporary spray mount to put it on poster board and set it for a kiss-cut so the board stays together and no pieces are lost. The biggest No-No I've learned when lasering leather is trying to squeeze out an extra piece or two from 'spongy' leathers. Those are going to shrivel up on you.