Most planner utilities are basically just glorified task-lists or calendars -- really just digital substitutes for those re-fillable 3 ring binders of decades past. They'll save you the cost of ink and paper refills, but not so much in terms of time and sanity.
For starters, Watership Planner reorganizes itself -- in real time -- based on the continual interruptions, changing priorities, and estimation slips that we all encounter every single day. Other planners force you to tediously move and re-position tasks whenever your schedule changes.