I can attest to this through the experiments in different guitar volume setting with my Les Paul's neck pickup. I tried some of the tips mentioned so far. If I start @ -+8 I can achieve my ideal amp gain tone at about 10. If I roll back to 8, it is not much less volume and there still is a hint of breakup, but if I pick more lightly, my tone gets close to “clean”.....but not squeaky sparkling clean. If I I start between 6 to 7, my result is a darker clean and not distinct. If I tweak my amp to comp compensate, then roll up to crunch, it means I may be too loud for the room. This scenario will vary from guitar to guitar, so my results pertain only to me. The overall goal remains the same and that is to achieve a good useable drive and a clean tone just by using the guitar's volume and tone controls. The other variable is your own definition of clean. For many it will be an amp just slightly breaking up and borderline crunch. Others won't be happy with that and wonder what they are doing wrong.There’s a lot of good info in here. I’ll add that, counterintuitively, I’ve found a good compressor to work well to balance the levels and pump the clean up a bit.
I'll also add that you're better off with the guitar's volume a little higher and picking lightly, than you are lowering it down so it's squeaky clean when you're heavy handed. That's how you enter the mud zone. Clean it up, and don't forget about picking dynamics, as you would with any clean sound.