Hello Sandro !
What I experimented is that as long as I stay away from musculare failure I can repeat a performance again and again without a decrease in performance (if fatigue is not accumulated). In example I could do 3x6x8RM wih 2-3min between sets and if I pushed the last set to failure I would probably be able to do 8 reps but if I did 1×8 to failure then my reps would drop on the next set and it could take days or even weeks until I would be able to do 8 reps again with that weight. If you don′t go to failure you can repeat the same performance within a few minutes so obviously you should be able to repeat it a few days later which is NOT the case if you go to failure.
So I believe training to failure makes an HUGE difference in recovery time compared to training short to failure but it doesn′t make an HUGE difference in muscular growth stimulation. You can stimulate growth without going to failure EVEN if you might not be able to stimulate 100% of the growth without going to failure. If you can stimulate 60% of the growth possible with one rep short to failure and can do it 2x per week then it′s better than going to failure once a week (and stimulate 100% of the growth possible). Even if you could only stimulate 40-50% if would be ok because you′ll decrease a lot the risk of overtraining and thus increase your chance of making long term progress.
All in all I believe training to failure to be superior (for stimulation) but it′s an ideal (a maximum dose of stimulation) and shouldn′t be done on a regular basis. I think it′ll hamper progress rather than increase it. When you are deeply fatigued/overtrained it takes weeks if not MONTH (at least for me it can takes month) to go back to your previous performances.
BTW I think going to failure with heavy weights is even hard on the nervous system because the nervous system have to recruit and fire more fibers at the same time ! In my case I recover much faster with a 10-20RM rather than a 1RM but I also think a 1RM provide a higher stimulation (more force generated/muscle activy per unit of time and less fatigue).