This is useful when you need to compare times across pools of different measurement units such as indoor and outdoor pools. For example a short course Indoor pool is 25 yards where as long course outdoor is 50 meters.
This calculator assumes constant pace and does not take in to account the pool length. So it is best used for shorter distance comparisons as the longer distances there will be fatigue which is not accounted for. There can be an advantage for some using smaller pool as you can kick off the wall more often. Even with these assumptions the conversion gives you a good benchmark for switching between pools.