For me it's brutal. I have Adult ADHD, and so compulsion is one of my worst enemies, and yet at the same time, my best friend. the smallest weird feeling about a drill (me thinking it sucked) will drive me to do it, for literally as long as it takes to fix it. That, however, is self-defeating, because as the practice wears on, stuff tends to go down the tubes anyway.
Forcing myself to mix things up is critical. Even in working out at a gym, the experts say "don't stick with one routine for a long time" because you'll develop muscle memory (which is, in that area, a bad thing)
In billiards, muscle memory is generally considered very good, and is linked/confused by most as "consistency".
The problem with that, is that there is a direct trade-off between muscle memory/consistency, and versatility - which is what is very valuable in league/competitive play.
I guess balance is the key.
The one other rule I must vehemently stick to is that you must focus on changing ONE variable at a time when trying out new techniques. If you change 2 variables, you'll never know which one was helpful. One session, one focus.