@Diederik,
We don't create many tasks in SF for that very reason but since SF charges an arm and a leg for the equivolent of a free USB drive, we're sensitive to fact that some tasks have value for a period of time. For example, we want to alert reps of a potential renewal but we don't care about tracking that beyond three months out or so after the task has passed.
I'd like to be able to create a task for reps to follow up, then delete them when they're X months old. Or delete any task older than X years (rolling cleanup).