So we all agree that 20, 30 or 40...100 reps will increase muscle and strength.
So is it efficient and optimal....clearly no.
imo, there is a strong relationship between muscle endurance and strength, although more so for those who do train with higher reps.
when I trained with a runner up in the nabba mr universe, I could easily beat him on reps on 100kg even though he smashed me on heavier weights. he trained very heavy with long rests; I trained with moderate weights, around 60-65% of my max, and short rests. that is why.
if you set your test for progress at 20 reps, which is around 70% of my max for me, then that provides as good as any test to measure progress.
I prefer a 10 rep test, which is around 80% of my max, to measure progress for most exercises.
having worked out my max from the high rep test, i then train on 60-65% of my max for 3-4 sets of 6-10 reps for a number of weeks before testing progress again after a deload week to help adjust training weights.
for example, when i could bench 10 reps on 137.5kg, which works out to around 172.5kg for a single for me, i still mainly trained on 110kg for sets and reps with short rests.