This is more a rap on the knuckles for past irrigation practices that failed to forsee the future, but back when, they didn't know there was anything wrong with what they were doing. Maxipaw/Minipaw heads, that are shooting well over 30 feet with 25 psi at the heads, on systems that can never have enough head pressure, regardless of gear-drive-rotor nozzle choice, to install a gear-drive in place of the impact heads. Older brass impact heads, with larger nozzles (like 3/16") that reach distances at low operating pressures that gear-drives won't match. Ditto for impact-heads that splashed water off to the side, and covered something important with that side-splash. Toro Super600s - some installs made every use of their distance capabilities, and when these things first hit the market, they had to appeal to folks that knew the brass impact heads they were using could absolutely cover a 40 foot radius. Think a Hunter PGP with a #4 nozzle can match a S600 PC1.3 for distance? Or any 1.5 gpm nozzle? Similarly with a S600 PC2.5, at certain pressures. Their higher trajectory was one reason, and the distance-over-uniformity nozzle design was another. Older PGPs, in some applications. I don't think Mr. Ed Hunter sold sprinklers with poor water distribution, even in the earliest days. But about ten years back the PGP nozzle designs were modified from the center-hole-plus-side-slot to the current rectangular hole, on sizes 5, 6, 7, and 8. A call to tech support got a response of "Yes, we know they don't give the same distance performance as they used to at lower pressures. But of course, you really want to have 50 psi at the heads anyway." (that's ever so comforting to hear, especially when the static pressure is barely 50 psi in the first place) ~ I think the modification has more to do with marketing, and competing with Rain Curtain nozzles, than anything else, unless clogging from debris was a factor. In any event, they should have left the original nozzle molds intact, so they could supply legacy applications. Various older high-trajectory rotors. I doubt that there are many still in use, but it was a real headache when it was obvious that some dead rotor was not replaceable with anything available, on account of the old rotor pitching the water up high with a 30 degree trajectory, and clearing some untouchable obstacle. Thompson rotor heads. If they still made them, they'd list for three hundred apiece. Anything from 4 gpm to golf-course-sized watering, depending on nozzles and stator selection. Another low-pressure-capable head you sometimes couldn't substitute for. Utterly unbreakable. By the way, if you look at the fixed-arc gear drives for a Toro 640 rotor, their angles are a match for the Thompsons.