I disagree. Throttling does not affect pump or impeller. Deadheading does affect pumps as the seals will heat up and be destroyed.
Do not dead head and you will be fine. If throttling was a problem then process plants would have gone broke about 90 years ago.
Yes, i have years of experience in waste water and process plants throttling pumps. This is not dangerous as our little pool pumps do not blow up.
Deadhead will heat up the seals until they leak really bad then they wont prime on restart.
While I agree that
in a professional setting with trained operators like yourself who have experience with the system, because
it is their job to do it right, might have no problem using extremely heavy duty, likely cast metal of some sort, equipment that can handle and may be designed for the abuse, a residential pool owner, who might look at his or her pool equipment once or twice a month should exercise extreme caution when playing with the output of a pump with a valve in the return line or between the pump and filter. If you've ever seen what happens to the sealplate on a residential pump, or the filter tank on a residential filter, with a throttling valve, you would understand. They are not designed for that type of use
If you have never seen or heard the results of a pump sealplate split or actually "explode" (fortunately it was under a house), separation-tank lid blow off, filter lid split or blow off, two-year old pump on a waterfall with the bearings screaming because it had to be throttled so far the water was blowing past the seal, you don't see that there is no connection between the two, a commercial plant and a residential pool.
Pool owners hurt themselves, mostly their finances, by damaging their equipment all the time, unfortunately, because they don't realize just how dangerous this stuff can be. Part of my job, as I have always seen it, is to protect the owners from themselves. Therefore, my warning it can be damaging and dangerous if not very careful. Also, unfortunately, "I want to vacuum to waste but not waste water," is a contradiction. Throttle the flow out and you get less suction, meaning you are vacuuming longer and using (wasting) a similar amount of water.