It is very important to warm-up at the beginning of a workout for various reasons. It allows a chance for you to mentally prepare yourself for the upcoming endeavor, stimulates synovial fluid secretion in the joints, and makes muscles, ligaments, and tendons more pliable.
On the opposite end of the spectrum if you warm-up too much you can fatigue your muscles unawares and not have the energy you should of had when you attempt your top heavy set or tried setting a new PR.
My recommendation is to do one really light weight to help warm-up the joints. And then a second warm-up that is no more than 50% of your top weight and don’t use high reps.
I am finding in time that the Bulgarian or Heavy Duty training done by Mike Mentzer is more fitting. The objective with this type of training is to do as few warm-up sets as possible to ensure you are properly warmed up while conserving all energy for maximal exertion on the top set.
A warm-up is not just a warm-up. It can make the difference between having a successful workout or not. It has to have a strategy or a purpose. A perfect example of this is The Burgener Warm-up done with an empty Olympic bar that teaches Weightlifting technique progression.
So the next time you warm-up think about making it a productive part of the workout. And keep in mind that the objective is to warm-up -not fatigue the muscles prematurely.