Were you around then? Techs who really knew how to properly mod a tube amp were rare, and if you could find one, it took forever..
That's the primary reason I learned to do it.
Fender tone stack FEEDING several more gain stages isn't intuitive for most to this day. Hence the millions of posts on boogies being difficult to dial in. Back then, it only existed on mesa and dumble. If you spent time playing a cranked to hell bassman, then you had some idea, but even 40 years ago, that kind of volume was frowned upon in most clubs.