re- graduations explained ?

[Adrian Levi]

I'm sure that there must be the exception ,for example a bass with an overly thick plate that sounds fantastic . Does anyone over here have such an instrument ? Also actual density of the top wood must be taken into account and may have been a valid reason for a luthier to keep a top a little thicker than usual.
I guess that the only reason to thin a top down must be in a last ditch attempt to improve on the sound of a poor sounding instrument after all else fails. And then what if (note I said 'if') a re-graduation actually makes an instrument sound worse , or introduces some other undesirable artifact to the sound