Prevent disused brakes getting stuck
Adding to the first part of mattnz's comment


  You should check they are working and adjusted properly by applying them a few times at the start of each ride, this should be enough to stop them sticking from lack of use. 


That, of course, applies to both brakes.

I would recommend using your rear brake more, since it's adequate for most braking tasks. I generally use both brakes in most situations. This gives me a good feel for how each is working, so when I really need them I have a good idea for what will happen. In emergency situations, though, remember that your front brake is 50% more powerful than the rear brake.

Another reason for ambidextrous braking is so that you can signal with either hand while braking. It has to be said that for most people this is a higher level skill, but you can begin to do it by braking gently.

But for completeness, I should mention that some people say the rear brake is almost useless. You can form your own opinion after reading what Sheldon Brown says here.