Well if you're talking about static stretches then that is a good thing. While increasing your ROM, static stretching also decreases your muscles strength which actually encourages injuries. However, dynamic stretching and warmups with light weight are always a very good idea. Warmups should also not just be "light" it should move through the range of weights that you will be lifting so as to acclimate you body to lifting heavy. Obviously you should keep the volume very low when the weights get nearer to your actual lift so as not to burn out before your actual sets.

IronWorker