Taking a break is crucial if you are pushing yourself to the limits when it comes to studying, doing work, or activities. It is very important to let your mind take small rest so it is not continually being used and for it to recover. It is similar to when exercising that you need to let your body take a break when you are working out. If you workout continuously without taking a break, it can prevent you from recovering and you would exhaust yourself at a much faster rate.
Most mental tasks you would probably have to do, you would most likely have to do that work for an extended period of time. It helps to make sure you are on task by taking those needed breaks.