either you are referring to drop sets or you are refering to deloads
drop sets IMO are wonderful. a lot of guys think they are a waste of time which is fine, that is their opinion. but i like to do them to reallly get a nice pump going
deloads are important to stay healthy long term, it is your way of giving the body a break, while still conditioning your muscles vs. just stopping weight training. lets say you were dealing with a nagging injury, deloading is a great idea because you won't stop lifting totally