Having done this to several vintage jap bikes, I'm not convinced. With notable exceptions (early 70s CB750 comes to mind), it generally improves performance if it has any appreciable effect at all.
In part, this is due to the fact that old Honda jetting erred on the side of rich - as you'd expect, given the fact that rich jetted bikes start more easily and fouled plugs are a minor annoyance compared with holed pistons. So in a couple cases I've found it actually solved, rather than created, issues.
Besides, in an environment where it's not unusual to fabricate tanks, build wheels, re-engineer suspension, etc., rejetting some carbs isn't exactly a lot to ask. It's a bit like saying: "Running is a sport best avoided." "Why?" "You'll need new shoes."
A