A blog called Trizle gives varies reasons why one big deadline wouldn’t work for large amount of cases, and why you must set a series of deadlines:
It gets you working now. It gets you producing kick-ass results at every stage of the project. It keeps you on track to getting the sucker done on time. It’s in the research.
The key is to break down into smaller pieces and set deadlines for those pieces. It is easier to achieve; It is easier to track; It is also easier to chase people on delivery. How to Complete Things on Time – [Trizle]
