Obtaining a 1 rep max is a great way to monitor progress in your training by comparing current performances to previous performances. It also allows you to work out submaximal percentages of your 1RM so that you can target different training zones. For example, you may aim for approximately 80% of your 1RM to work on muscular strength at the start of a training block.

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The benefit of using a calculator instead of doing a full 1RM test is that it is arguably more practical and safer to do on a regular basis and with those who either have no need to train to their absolute max or who are relatively new to the gym.