I've used sarm s4 5 times now. Once as a stand-alone while doing a recomp and 4 times during pct. For pct I'd say that using it I retain 75-85% of my gains (at least) vs 45-55% without it. It is definitely worth it. I start it as soon as I quit injecting and take it till I start again. 50 mg/day 5 days per week.
For example: I once did a bulking cycle, 12 weeks, gram total aas and went up to 235 lbs. After I came off I crashed and went all the way down to 205 lbs without trying hard to lose weight! That's a crash without s4. I re-tried the same approach next cycle but incorporated s4 and again I went to 235 lbs and when I came off I went to 223 lbs- and that was after switching to a ketogenic diet. If you consider that about 8 lbs is generally water weight (comes off as soon as test clears), that's not bad.