I train primarily for muscle growth.
For my upper body the effective range for encouraging growth seems to be quite narrow. About 7 to 11 reps (forearms notwithstanding), moderate bar speed, pretty strict form, full range. When I get beyond 11 I don't see any more growth.
For legs I don't see any growth below about 11 reps; the sweet spot there seems to be about 15 reps.