Consistency is a major factor in pretty much any sport. It's difficult to improve your performance if you don't have a consistent baseline from which to diverge, just like how you change only a single variable when using the scientific method. I know little about tennis mechanics, but I imagine a hypothetical experiment could be something like "Do I get a lower bounce if I put the angle the racket slightly later during the swing?" Being consistent is the first step to being able to test that theory.

Gathering data during practice and play allows you to know if you're being consistent, and if you're not, when those inconsistencies occur. Once you've hammered out the inconsistencies, you can start to experiment and improve your technique.

Weight lifters make meticulous notes about their workouts. Even amateur race car drivers spend thousands of dollars on data logging equipment. Professional sports players spend hours watching videos of themselves. At a high level, it's all about data and analysis to provably improve technique.

I am not questioning the value of data collection... I guess I am more questioning the data quality and applications.

I suppose it's less relevant if we agree some data is better than none. I also wonder about the relevance to the weekend warrior. Is this something that really will improve their game? Or is it just a fun way to engage in a hobby? Maybe it doesn't matter from a market viability standpoint.

> I also wonder about the relevance to the weekend warrior. Is this something that really will improve their game?

Yes, if they're interested in improving it. For basically all the reasons coldpie has already pointed out. It's true that you'd need to practice specifically as well as play games--it's much harder to develop higher consistency from the dynamic environment of a real game--but that's not unusual.