At the end of the quarter, with exams looming and deadlines imminent, there's always the feeling of "Damn, I could have used that hour. I wish I hadn't wasted all that time last week on --------." It's in those moments that I wish we could bank free time and use the roll-over minutes when we need them. Instead of procrastinating on YouTube, I'd just make a deposit now and jump forward to the next assignment.
However, if we were actually graced with such a beneficent arrangement, it'd probably be a good idea for the Universe to impose a limit on the use of roll-overs per project. Otherwise, you might accidentally use up the precious minutes where you could have saved the Titanic, on a problem set -- and then really regret it