Performing the full range of motion (ROM) of every exercise for every rep is far superior than partial range of motion and a “good” time or finishing before the person beside you. You only develop strength within the range of motion that you train. Additionally if you do not complete the full range of motion for a given exercise you may not be developing all of the muscles that you could be. For example the squat. If you only do half squats or you don’t get the crease of your shorts below your knee caps you are completely neglecting your hamstrings and glutes (butt). Performing partial ROM of exercises can also lead to injury because you will create an imbalance in the development of muscles.
Full ROM will lead to superior results, period. Initially your times may suffer and you will not finish as quickly as everyone else. But as you develop and strengthen your muscles in the full ROM your performance will increase far more effectively and you will become a much more balanced athlete.