I generally use both brakes whenever I am stopping or slowing down, regardless of my speed and whether its from coasting or in a panic stop. The front brake actually checks my speed and the rear allow me to control of the bikes attitude. I often apply the rear slightly ahead of the front, especially in slick conditions or when in a turn, but even then I will use some front brake to reduce speed. In fact the only time I don't use the rear brake is when I am doing a stoppie (nose wheelie to you motorcycle types), and even then I will often apply just a bit of rear so that I can better feel when the rear wheel lifts off the ground.

To be honest I've never known anyone to use only the front or only the rear brake except for noobs.