Manu-wah???
Seriously, while the game is playable without a manual (especially if you've played OOTP), it would still benefit from one, particularily for some of the mechanics that aren't in OOTP.
Workout strategies (e.g. which Flex routines are more important for what type of player), drinking consequences (obviously drinking affects your game, but by how much? Whats the performance difference between a slight or terrible hangover?), etc... I have no problem with the general idea of how they work, but if I'm to optimize my player's development, I need more specifics on *exactly* what each feature affects.