You need to when you are facing these power forwards in the heavyweights. I'm a prototype like Evander was earlier. My added weight is all muscle. With more muscle, comes more power. I will be able to throw harder shots with more behind the punch.
Heavies nowadays are freakin' huge.
But your strength has always been your mobility, your speed. I move around as fast as before. The big change will be that my punches carry more authority. I can't stay small. Look at Joe Frazier.