Focusing at a specific intensity at a certain meso vs having a rep range. E.g:
Scenario 1:
Week 1: Squat 3-5 sets x 10 reps
Week 2: Squat 3-5 sets x 8 reps
Week 3: Squat 3-5 sets x 6 reps
Effort level is at RPE 7-9. Load is adjusted as needed to do the prescribed number of reps without reaching RPE 10. (Typically powerlifting, peaking)
VS.
Scenario 2:
Week 1: Squat 3-5 sets x 6-10 reps
Week 2: Squat 3-5 sets x 6-10 reps
Week 3: Squat 3-5 sets x 6-10 reps
Effort level is at RPE 7-9. Load is adjust only when the rep count performed goes above or below the rep range else, the load stays the same. For example:
Set 1: 150kg x 10 reps @7
Set 2: 150kg x 8 reps @8
Set 3: 150kg x 8 reps @8
Set 4: 150kg x 6 reps @9
Apart from the obvious: “just be consistent and both will work”, does one scenario offer unique benefits that the other doesn’t?
Population in question: general population who just want to build strength and muscle, no plans to compete.
I don’t think we have strong reasons to believe one would be markedly superior to the other. The latter setup you describe is sometimes known as “Double Progression” and has been around for a long time. I tend to use that strategy more for my accessory work, whereas I tend to use firm rep targets for my main/competition lifts. Not saying this is “right” or “wrong”, but just my preference and is sometimes how I program it for others as well.
I also tend to use the former setup for my more specific work and a more flexible range for my accessories. One rational for this is that I don’t want to be thinking about RPE/RIR during a set of my main work, I want to be focused on the execution of each rep. Whereas I am less concerned about intent and efficiency during accessory work (especially simple isolation movements) so I can more comfortably let myself evaluate RIR intra-set. I also tend to program accessories closer to failure and figure that for hypertrophy a set is a set (Basically I believe the hard sets model is a good way of gauging the hypertrophy dose for the way I set up my accessories). For my specific work I’m more concerned about the total number of reps I’m performing, because it dictates the amount of practice I’m getting and because the higher relative load I’m using leads me to think that the total number of reps has a more influential role in the hypertrophy response. If you want to vary the number of reps per set on your main work but agree that the total number of reps is important, a strategy you could use is prescribe a load and total number of reps to be accumulated (such as 15reps at 80% in sets of 2-6). I think this third option can be a good way to manage fatigue within a workout while maintaining load and volume, allowing you to accumulate high quality reps at a given load regardless of normal fluctuations in fatigue (if you’re carrying more fatigue going into a workout or it accumulates quickly within the workout you can just break up the volume into more sets). I still wouldn’t try to precisely rate RIR during a set, just terminate the set if rep quality or bar speed drops noticeably. This does require that you have the option to take extra time to rest during your workouts.
Also my reservations about trying to rate RIR intraset probably isn’t an issue for everyone and you could potentially work around the issue with a velocity track or perhaps a very attentive training partner or in person coach.
You said it yourself, either can work (and if you’re not planning on competing you probably won’t notice a difference that you care about) and any unique benefits are probably quite small (just finding something you’ll do consistently is vastly more important) and subject to individual variation and influence from other programming parameters. I like to have a little story or mechanism to go along with my decisions, but the true deciding factor is I’ve tried both and have some data indicating what works for me (more flexible approaches to my main work has been associated with worse e1rm outcomes, but it does seem to have been a helpful strategy for rehab)