I know you are asking CT, but I would never recommend anyone using single reps as a training strategy for either bodybuilding or powerlifting.
But I have trained at around 80% of my 1 rep squat max where I did a single squat every time the second hand hit 12:00 for 10 sets. I did this on a light leg day and nothing else concerning legs. I believed that improved CNS recruitment. (BTW, I did not walk out the weight, leaned the weight out of the power rack. It takes a little practice to perfect the lean out.)
The way I do it is to use an approach built on extended/giant clusters. And approach that I’ve written about before and that got former World Strongest Man Marcin Licic.
Essentially you select a duration for your exercise (typically 10, 15 or 20 minutes) and a load (around 90, 85 or 80% depending on the duration) and the goal is to get as many quality singles in during that time. You progress first by trying to get more singles in during the selected time period.
You can get some size with singles, simply because any rep above 80% is an effective rep, even if it’s alone in its set. With this approach it is quite possible to get 12 to 25 singles on an exercise, which does represent enough quality volume to stimulate growth. But it will NOT be as effective as regular training for size.