I like to measure anything that matters and this clearly matters. Plus if you want to get buy I from your pitchers if you can show them on video the direct correlation it will go a long way. Plus we have to remember our target audience here. I went to school with a guy who had a 15 year career in mlb. One time 20 game winner. He was a great athlete who could roll out of bed and beat you. He threw incredibly hard at the age of ten. People from the community came out just to watch him from the time he was about 12. All the things we are talking about just came naturally for him. I would not want to time or Even video him when he is throwing 97 in high school. But what about that kid throwing 79 who we are trying to get to 85? Or maybe even a tick or two more to make him recruitable? These kids have serious flaws including not getting down the hill quickly enough. If you can show them and explain to them in definable terms what is holding them back... then provide a method by which they can set a goal and measure their progress I think it helps. Rather than just saying "you are at 79 and we need to get to 85" I would rather break down what we need to do to get to 85 then show them incremental improvement along the way and how it directly relates to what we are teaching. This of course includes a lot of things mechanically not just speed down the hill.