If size of cut didn’t matter (not in a confined area), wouldn’t a thicker cutoff wheel last longer? I was comparing mainly between a 1/16 and 1/8 width wheel. I was trying to compare between cutoff wheels that you can get at Harbour Freight vs what you would buy at big box home improvement stores. Also, do the diamond cutoff wheels work that much better than masonary wheels?
Cutting disks should be thin. Grinding disks are thicker. Thicker disks means removing more material, which takes more time. Typical disks in Europe is 1mm thick, and I'd categorize a 1/8" (3.7mm) as a hybrid, usable for both cutting and grinding, but not excellent at either.
A thinner disk also leads to less heating in the material cut, as less energy is deposited.
In addition the disk should be made for the material you're working with. Different materials behave differently.