@ Kal, so instead of doing let’s say two straight sets with the same weight. You prefer to work up to a single top/Heavy set and then do a lighter set(s) as a back off set(s)?
This is how I often do it, here is why:
1. My first goal is to warm up the joint, the goal here is to not tire out the muscle and not put wear and tear on the tendon(s). 1st and maybe 2nd set. (Often skipped on subsequent exercises for the body part.)
2. My second goal is to prepare the tendon for the for my heavy set, reps will be lower because I want to both preserve muscle strength and minimize joint/tendon stress. If necessary, I will wear the muscle out a little bit if I feel it is required for safety for that particular lift. I do 1-2 sets like this closer to my working set range.
3. My third goal is to stimulate an adaptive response in the target muscle(s). This is my all out set, this is the only set I probably do forced reps on, or a drop set, etc. I go to "failure" but I'm in a mindset relative to how hard I think I should be pushing myself at that time, so it's all relative based mainly on injury prevention.
4. If I'm not done at this point, I may want to do a second lighter set. I know I won't be stronger than my all out set and even if I was just as strong, why would it help to signal the same adaptive response again? Are you thinking you are recruiting unused motor units of fibers? Unlikely, and if you are, you would with lighter weight also. I'm only talking 10-20% lighter. This is a great way to get better at the exercise, increase mind-muscle connections, strengthen connective tissue, possibly improve blood flow to the muscle. The problem with the second set is that it can make you much weaker on subsequent exercises, so I usually skip it on the first exercise for each muscle.
If you think about it, I think this is pretty much the basic ideas behind everyone's training for the most part.