The park can gleam more from this sort of data than you'd think. They can gleam information about guest flow around the park, ride throughputs, what rides guests are using, the most popular rides, what demographics are using different rides, what rides certain demographics are riding most... the opportunities are endless!
In terms of the uses for this data; the park could use it for all kinds of means. They could ascertain where the knife should fall when planning things like staggered openings, for instance, and they can also see how well ride operations are doing, how accurate queue times are, see what certain demographics are enjoying, see what the guest populace as a whole is enjoying... there are all kinds of reasons why a theme park might want to know this sort of data and gather it on a large scale.
With that being said, I agree that there are probably less costly ways to do so. Alton Towers had technology that probably did most of the heavy lifting for this sort of data collection as long ago as the mid-2000s, when they did that DVD thing that was basically a spycam... wasn't it called YourDay or something like that?