"reinforces the top side with choshi."
White plays kikashi with - before playing . Now the game depends upon Black's attack on White's central group.
By taking profit in the corner with White considers the exchange of for choshi, but in reply, provokes , also choshi. (i.e. White shouldn't play this way.)
This example comes from 21st Century Go, vol. 5, p. 229, by Go Seigen.