The style determines the plays that are in the playbook - a run style offense will have more running plays, west coast will have more short passing plays, etc. The style also determines the default attribute weights to make the composite rating (i.e. a run offense coach doesn't value the QB as much as the RB). You still control what plays are called and also can always override the coach's opinions about the attribute weights, so what it really boils down to is the plays listed in your playbook.