It would be very cool to have an opportunity to stop time when it was necessary.
It would be very convenient, when you are late, or perhaps it is necessary to do something and there's no time to do it. It would be very convenient for students during sessions when they should prepare for examinations at nights. Businessmen who always have a lot of things to do would also appreciate this invention.
And it would be very cool to study foreign languages with help of this invention. The sense of that you have a lot of time, and you will certainly do everything in time gives you the real freedom. Though off course, it is absolutely not real. And it is a pity.