I always forget the importance of taking breaks, so I'm writing this to remind myself. Breaks are helpful for two reasons:
The second reason may be even more helpful than the first. A thoughtful break can save you from spending time on things that you don't want/need to do. Often, the best thing to do is be lazy and think about what you can not do, instead of rushing to do everything.
The evidence for this claim comes from a single anecdote: Today I was writing a simulator program (for a class) and trying to think of ways to make it faster. I had set my mind on one or two ideas and I was just about to start programming, when I felt that I should really take a break. I had been programming uninterrupted for a few hours and evening was falling. So I went for a walk and kept thinking about the program. I concluded that neither of my ideas would really improve performance dramatically, and would make the program considerably uglier, so I decided to do none of them. I saved myself a few hours and got some quality time outside by taking a break.