A lot said here but let me take this apart somewhat..
Take two doors, make a set of ribs and shape the doors and glue them to teh ribs.. Barbaric as far as making a bass, right?
Well, many factory basses made and even some by hand were poorly graduated if at all. In this case, re-graduating is more a case of
'completing' the build of the bass since whatever shop, factory or person that tuend out this bass shaped doghouse didn't. So, you are just finishing the bass as if you bought an incomplete 'kit' that you finish at home.
That's one scenario..
Another is a full handmade bass that is left thick or un-even in some areas. In this case, the 'skilled Bass maker' (please, not just someone who fits bridges) careful does 'spot' re-graduations to correct a few areas that were left thick and might be dampening the sound of the plates.
I had one bass that was a masterpiece but made by a Violin/Cello maker. The plates were about twice the normal thickness. The arching was fairly high especially the back and the wood strong, dense, beautiful and just too darn thick. In this case we opted (the maker and me) to re-graduate the bass to about 20% over normal thickness just to be safe. The result was more depth than before, the bass was still ultra strong and the cutting power as good as before or better. This was an old bass with no cracks on the top and a mint condition round back.
The feared and last situation is when some wannabe or some real luthier thinks he knows more and takes a good bass and butchers it thinking he can improve a masters work. About 40 years ago I was talking to an old time pro from a top pro orchestra. He had an attributed 4/4 Maggini. It went in for repairs and the luthier notice that the top had a raised platform under the bassbar and around it like a deliberate support graduation. The luther at this point decided he knew more than Maggini according to the owner of the bass and shaved this support area away, gone. Made a bassbar (probably hugely sprung in as well) and delivered it to the owner. Soon after, the Top sunk from the alteration. The sprung bar (which this shop is infamous for) surely helped this sinkage to occur even faster. Butchery at its peak!
Now, as far as players go or whatever, I will leave that out of my response here. I just wanted to clarify that the graduations of a bass can be corrected at times and ruined as well at other times. When carved out too thin, new wood must be added back in and then hope for the best. I have owned basses that were restored for the better both ways from too much or too little. I avoid the big shops that might do the wrong thing or not give enough personal care or attention to detail.