Former MCSL President Sally MacKenzie once described Time Trials perfectly:
"Why hold time trials?
First, it lets the coach determine the first "A" meet's lineup. Lots of things change over the summer--kids grow, start (or stop) winter swimming, age up into longer events, etc.--so last year's times don't always tell you how fast a kid will be this year. And, of course, if a child is new to swim team or is swimming a 50 instead of a 25, you don't have times for him or her at all.
Second, it gives the swimmer a starting time that he or she can work to better over the season.
Third, it gives children new to swimming--and those who may have forgotten over the winter--the experience of swimming in a meet. New swimmers learn how to report to the clerk of course, how to line up for their events, and what a starting machine sounds like. They get an introduction to the sights and sounds of competitive swimming--and they also get to check out the snack bar.
Time trials is also great for parents, giving them a chance to learn or remember what they need to do at meets. It lets them brush off their rusty timing skills or figure out where the team's coffee pot went over the winter. New meet managers and team reps get a practice run, hopefully making the first dual meet go more smoothly."