I think this feature is useful in many levels; in business it will give insight on each project and the time it took while working, thus estimated deadline, and individuals such as freelancers will be able to determine the time each project requires so they can price their hour cost.

The timer will pause while the project is open but there are no changes.
This feature is not only for After Effects it may be implemented in most of adobe products including Premiere, Photoshop and Illustrator.