Performing a higher proportion of repetitions within two repetitions of muscular failure enhances hypertrophic stimulus efficiency, resulting in equivalent muscle growth with fewer total repetitions.

Study: Effect of resistance training to muscle failure vs non-failure on strength, hypertrophy and muscle architecture in trained individuals

This study found that lifting weights until you're almost too tired to do another rep builds just as much muscle as lifting until you can't do any more—meaning you can get the same results with less total work.

Study: The effects of resistance training to near failure on strength, hypertrophy, and motor unit adaptations in previously trained adults

People who lifted weights almost until they couldn’t do another rep grew just as much muscle as those who stopped earlier—even though both groups did the same total amount of work. So, going close to failure can be just as good for building muscle without doing more reps.

Study: Effects of drop set resistance training on acute stress indicators and long-term muscle hypertrophy and strength.

This study found that doing just one tough set of lifts until you're almost too tired to continue grew muscles just as well — or even better — than doing three easier sets, meaning you can get the same results with less work.

Study: Effects of Drop Sets on Skeletal Muscle Hypertrophy: A Systematic Review and Meta-analysis

This study found that lifting weights until you're almost too tired to continue, then making the weight lighter and doing it again, builds just as much muscle as doing a lot more reps the normal way—so you can get the same results with less work.