I'm with Polyhive. I have not fed anything this spring. Been close on two or three occasions. A beek less than four miles down the road said he had been feeding all his bees since January right up to the warm patch in May. They for sure had not collected a great surplus of honey, but none have run completely short.
But I have a very good idea of what they have, and are doing. New beeks don't, so it is better to feed than not - if not sure. Dead colonies do not recover. But feeding when it is known that stores are present is, as PH says, a waste of money, and is counter-productive.
Nucs should be provisioned with adequate supplies and they should simply be a smaller version of a full colony - so if you are feeding nucs, you should also be feeding bigger colonies. You don't need to inspect to check if stores are present - roof off, coverboard off, check stores frames and close up. Hive open less than half a minute on most occasions. I call that a check for stores, not an inspection and I would do that as often as necessary to a sample of colonies if not sure. I watch the weather and have a good idea if they are foraging, by the bees' activity.
Collecting water means using stores. Warm outside and bees flying afar means bringing back forage. It may be mostly pollen depending on the time of year, but forage crops do not usually change abruptly from one day to the next.
I stand, or sit, and watch my bees at times. Fascinating, but if you are watching you should be checking, understanding what they are up to, cross checking later, maybe, to check what your observations told you. It doesn't take long before you can estimate the stores levels going in sufficiently to guess that change is + or -. It's not rocket science, just simple observations.
If the hive is gently humming in the evening you can bet it is heavy with nectar being evaporated down, ready for the next lot. I estimate my field colonies from my local hives. Most years, by now, it is irrelevant - they have plenty of stores and it may be starting to diminish, but this year has been difficult. Unprecedented, in fact.
Some on here would do well to do a search on the amounts of nectar (or honey equivalent) that a colony gets through each year, before even storing any surplus. That 20kg left for over-wintering is peanuts in comparison.
added : Agree with Finman, too.