I'm not trying to be rude but why? If info is available to us than shouldn't we try to use it for our benefit?
You aren't rude to ask. I think, unless you have a PAR meter, it is hard enough to try to get close to a good PAR for your tank and the type of plants and growth you want. We don't even have very specific information about what "good" PAR means, especially since the PAR experienced by the plants depends on where in the tank the plant is, what part of the plant you are concerned with - the shoots at the substrate vs. the tops of the plants, for example, and how much shading you have in the tank. Just getting that in the right ballpark takes a lot of experimenting.
Measuring PUR isn't something we can easily do - I have never seen a PUR meter. So, at best, we are guessing on PUR, based on spectral data provided by the light manufacturer. This is an aspect of planted tank keeping that might be very interesting to some people, so of course they should do what they find interesting. But, for an average planted tank person, with average experience, it just seems to me to be an added confusion factor. If you can't even be sure how much PAR you are using, concerning yourself with PUR doesn't seem to me to be a benefit.