It's quite useful to see when you want to see the actual usage of particular words.
You can look up sample phrases from several different sources such as fiction, magazine, and spoken.
For example, I've just look up the phrases "no less than" and "not less than" and it turned out to be "no less than" is 10 times more often used than "not less than." oh well, so what's the point for English learners of beginner level to learn both phrases at the same time in Japanese English textbooks..
This corpus could be an easy tool for English teachers to make sample sentences to use in the class.