I agree. Each tool has a different (cutting) thickness. I've got
scrapers that are very thick (1/2") and some that are much thinner. I
wouldn't think of keeping the tool rest at the same height when I
switch from one to the other. Nor would I set the tool rest the same
for a 3/8" bowl gouge and a 3/4" bowl gouge. That's not to say that
I'm obcessive/compulsive about the exact height. I just bump the tool
rest up or down depending on the tool.