No matter what weight division weight training is beneficial but not at the expense of your normal boxing training.Basically it's all about balancing your workout plan.Sit down and think about what you need to work on in the ring.Every individual would be different and have a workout plan specific to their needs.Floyd Mayweather is a speed fighter primarily, but he also has power.So Floyd works a lot more on skill training than weight training.Whereas, Ricky Hatton is a pressure fighter who bangs and also has stamina, so Ricky hits the weights 4 times a week and does roadwork 6 days a week.So basically whatever work you put in is what you get out.But remember Sparring is the most important training as a fighter.There are fighters out there who do nothing but spar, nothing more nothing less, a la James Toney.James Toney has incredible boxing skills but he always could have been in better shape.So it's Checks and balances my man.Good luck with your training.