As near as I can tell, it's up to the player when to use their Exhaustion and/or Madness talents, with possible GM veto if the talent doesn't really seem to apply.  Whether it's a minor or major use depends on which sort of bonus you're trying to apply to your roll.<br/><br/>With Madness talents, the more powerful the effect you're trying to get, the more Madness dice you have to roll.  Guess what that does to the odds of Madness dominating?   >:)<br/><br/>