Thinking outside the box is commonly used metaphor for creativity or coming up with new ideas. Some problems indeed require a new perspective to get them solved. But sometimes the box is all you have. You are inside the box and there is nothing out there.
Working within limits can boost creativity as well. When you have limited resources you need to come up with new and effective ways to use those scarce resources. And keeping inside those limits often lead to more efficient solutions as well.
Of course there is a limit of creativity and effectiviness in both ways. The 200 word limit for these posts is an excellent example of this. It offers enough space to lay out a single idea or concept. Sometimes less words are enough, but not much. Same with going much over the limit: then it would almost require a multiples of the amount. Either adding another idea to the mix, or diving deeper to the single subject.
Until now, the 200 words has been the absolute lower limit due technical reasons. But starting today, there isn't such limitations anymore thanks to @basilesamel. I have always aimed as close to the limit as possible and now I can also do it from the other direction.