Another point that popped in my mind:
I also use a lot of materials that glowforge will more than likely NEVER sell. Therefore I will be out of luck if Im not using a proofgrade analogue. Not to mention I either have tons of scrap or can run to the hardware or exotic woods store on a moments notice and get what I need instead of ordering something online and having to wait. While Im sure proofgrade will be cool, I cant see myself using it more than whats available locally. The formulations for most of these materials arent going to be any different.
Not only that, but even with certain materials I might want to change the kerf for the last piece. For example: EVA foam. When hit by heat it contracts. If I was building a multi-layer object out of EVA foam, I might want the top and bottom pieces to be hit with a heat gun to seal up the cells before coating it with plastidip. This will cause them to shrink and be a different size than the rest of the pieces. If I can manually adjust the kerf for these two pieces, or have a setting called ‘heatgun shrunk EVA’ ive saved in the menu, I can just select that and be on my way for the top and bottom pieces. No more bouncing between software EVERY TIME I have to cut multi-layer EVA.
A manual kerf just makes sense.