PROBABLY THE BIGGEST DIFFERENCE between agile and more traditional project management approaches is in the area of planning. There's a misconception that agile projects do not require planning. That is not the case—they require just as much or more planning; it is just done very differently.
Traditional, plan-driven project management approaches typically attempt to do more of the planning prior to the start of the project, while agile project management approaches typically defers planning decisions to “the last responsible moment.” By the last responsible moment, we mean the latest point in time that a decision can be made without impacting the outcome of the overall project.
That is what is called rolling wave planning:
The thinking behind that strategy is that attempting to plan too far in advance naturally involves some amount of guesswork and speculation. Quite often, that speculation is wrong and will result in wasted effort in replanning later, and it might also require reworking any work that has been done based on ...