From what I know increasing workload for match preparation increases how quickly your players learn the tactic you've specified, and increases how much you train that week for "Offensive movement/Defensive positioning" etc...
However doing so decreases the amount of time your players spend working on their individual stats. Think of it as if you were a coach who has 1 week between games, you only have a certain amount of practice time, do you spend it learning tactics, or spend it in individual drills.