The short answer is you don't need one. The longer answer is, depending on a lot of other factors, it could be quite useful ;Wacky
There is no definitive list for the proper PAR for any specific coral. That's just totally unreasonable. As for a relationship, yes. Some corals are known to like higher PAR, some are known to do just fine in low PAR and some are highly adaptable to most any sufficient PAR. And understanding what your PAR is at different depths and different areas in your tank can prove to be very useful information (if you worry about such things). I've tested tanks where the highest coral in the tank was getting PAR levels over 400 and and corals on the sand under the shade of a rock ledge were getting PAR levels of under 50. Also, getting a new fixture, especially an led fixture, can be a real crap shoot in terms of peak PAR and spread of PAR over the length and width of the tank.
Is all that really super important? Probably less than most other things we measure related to our tanks. Is it useful? Well, it depends on how OCD you are! ;Nailbiting As well as a bit on what kinds of corals you keep (especially if you keep a real mix). And what kind of fixture you use and what the rockscape in your tank looks like and even how deep your tank is. But if you can borrow a PAR meter and take readings in your tank and draw up a map of PAR levels, that's probably all you'll need it for. Until you change something.
I've owned one for a long time. And I've used it on 7 of my own tanks in that time. I got it to know when my old power compact fluorescent bulbs needed to be changed. Turns out it can't really do that as the issue with fluorescent is spectrum shift and not PAR levels. But when I switched to leds about 6 years ago it came in very handy. Now I don't use it much, but when I do, the data I get is fairly helpful. And I've been able to do a lot of helpful testing of other peoples tanks over the years. Again, especially when they switched from MH or t5 to leds.
