From publisher blurb:
The monster design guidelines in the core rulebooks state openly that they’re only an approximation -- Gamers have described those rules as ‘rough’ at best and ‘crudely unbalanced’ at worst. The golden design standard of ‘N + Level’ creates inconsistent monster statistics, and in addition, the original designers themselves ignored their own guidelines most of the time, as many monster statistics presented in the core books seem arbitrarily assigned.
Monster Maker is a design kit for creating monsters in 4E. Instead of creating inconsistent and unbalanced encounters where players are repeatedly missing and getting pounded upon by foes who consistently hit and dodge incoming attacks, these optional rules are for Game Masters who want more exciting and faster-paced monsters for their players to fight.