Dear Boxing Fans,
Training for a fight is where the focus on styles must take place. A boxer and his trainer must focus on the type of style that the upcoming opponent has and adjust their own style to be most effective. This adjustment must take place in the gym and be hammered into the boxer so that it is second nature. This is in contrast to the way many boxers train in that they either focus on a strategy (eg. working the body more, using the double jab, etc.) or attempt to change their own style 180 degrees, with disastrous and comical results (see de la Hoya v. Trinidad rds. 9-12 or Tyson v. anybody with talent in the last 15 years).
Styles must be adjusted and not changed. All styles have their benefit and their weak points. The key is to understand the opponent's weak point and deliver. The key is also to understand one's weak point and then create a strategy to overcome that deficit. Had de la Hoya understood that his weak point as a puncher (almost a boxer-puncher) is a lack of upperbody movement and adjusted for that, he would not have been hit so cleanly and so often by a boxer-puncher like Mosley --and maybe, just maybe, would have pulled a win in that second fight.
In preparing for a fight, the boxer and trainer must look to his opponent's record and evaluate to whom the opponent has lost and what style that opponent had trouble with. With video all over the web, that is much easier than before. The boxer and trainer must then adjust his style -- more upper body movement, more jabs, early body work, etc. -- to be most effective. Only adjustments, and not style changes, truly work as the body's mechanics tend to change only a little at a time and revert back to what it knows and has done if too large of a change is attempted.