I use it myself at least weekly. I also use it to help other people who are curios what kind of par X light is at what distance. I has helped me to figure out that Hydroponics T5 fixtures are fine over a frag tank and fuge and still put out massive amounts of light at shallow depths.
I also used it to tune in my Halides over my new tank... I was 550+ over the entire bottom and I do have a few that acropora I like to be around 350 with (Dragon Varieties). They would have been fine under 550+, but their color would not have been as rich. The other stuff that I keep is fine up to 750, or sometimes, more, but I did need a few places where it was lower. I angled the reflectors where I had some lower light spots, but also an area in the sand where I was at about 625 where I can put my clams.
The main thing that I use it for it help folks who get coral from me find a place where they can put it in their tanks, or at least know where it came from. Example, trade a LE Blue Matrix the other day... put the sensor right next to the coral at 475 PAR. Let the guy borrow the meter... he was 275 to 310 all over his tank... he is thinking about different lights, but at least he knows that if it looks different, one of the explanations might be 200 PAR difference.
