There are different reasons why you quantify that time dedicated to certain tasks is more or less important. Especially if you work freelance or are self-employed. Of course, as students may also be interesting to have a sense of time that we consume in each task.
If we saw a few days ago we showed you today RescueTime similar application. Tyme is an application that allows us to keep track of how much time we used to perform a task or projector. All with a simple interface for us to focus on what really matters, do.