Firstly downtime is reduced to a minimum. Instead of refilling and starting from cold all that is needed is to refill the water reserve tank. The boiler does not need to be de-pressurised and steam is produced almost immediately, meaning downtime is merely a few seconds instead of a few minutes.
Another advantage of continuous flow machines is that the boiler itself can be a smaller volume, so giving even faster heating times, and longer running times can be achieved by increasing the size of the water reserve tank.