These exercises require several muscle groups spanning at least two joints to work together to get the job done. If even one of them isn’t up to the task (e.g., because it's fatigued or not yet strong enough to pull its own weight), the rest of the team (read: your body) suffers, leading to sub-par performance and sub-optimal results.

Skew the balance of the exercises in your training plan toward compound exercises, performing the most heavily loaded ones and those that place a premium on relative strength (e.g., pullup, chinup) at the beginning of your workouts. That will ensure that every muscle involved is able to exert its full strength.

But don’t discount the value of isolation exercises either. Sometimes laser-focusing on a single muscle group is exactly what’s required to bust through a plateau, jumpstart hypertrophy, or strengthen a weak link that has been holding you back in a compound move.