I ferment in a chest freezer with a temp controller, so after a week or so at fermentation temps, I'll turn it down to 39 degrees for a few days.
This helps drop the yeast out of suspenstion which leads to clearer beer. It also helps pack the yeast cake so when I move it from the freezer to my counter for racking, it does not get roused up very easily. It also stays packed on the bottom when I open the spigot to rack to the keg.
Here's what crash cooling does. This was leftover when I racked my Oktoberfest last week.