It's not about the stimulus. It's about the fact that some exercises are naturally better done within the lower rep range (5-10), while others work and feel better with the higher rep range (20-30). Some are better in the middle.

With DB side raises, take too high of a weight, and you will feel like you can't do anything productive done (can't even raise to an appropriate height). With lower weights you can get a proper range of motion and can really feel the burn and get the target (sic!) muscle exhausted.

Additionally, too high of a weight doesn't feel good on joints.

Similarly with squats (or deadlifts). Squating with 5-10RM is fine. But 30RM?.. Theoretically it gives the same stimulus as doing 5-10RM, but practically everyone who suggests putting such sets to a program should be medicated and put on a suicide watch. The taxationvon all systems of your body is just so huge (especially the more advanced you are).

Heck, mere squating true (!) 20RM (just one set!) is considered a crazy challenge that most will never do. I have done crazy stuff in my life, but I am not embarrassed to admit that this challenge is beyond me. Simply doing 20RM leg extensions is hard enough for me.

These require the practical experience. Take barbell/dumbbells, try yourself and no more explanations will be needed.