Although I recommend keeping 5 minute chess to a minimum there are some useful drills that you can do at this speed. Recently my son Sam and I have been doing the bishop and knight mate against the clock with us competing to get the best time. And other basic endgames such as queen against rook or rook and two pawns against rook are very suitable for this.
These technical drills are very good ones to practice at speed as the winning techniques can be remembered. On the other hand if someone plays too many full games at this speed they can develop habits that can hurt their long play chess in which cogitation is required to come up with plans and check for errors.
Of course bullet chess (one minute per player per game) is very popular, especially for those who want to take their minds of other things and then hopefully relax. But people are kidding themselves if they think this will help them improve.