Many use the rear remotes to power their backhoes, log splitters, hydrualic angling rear blades and much more.
There are a multitude of things, quite a few common ones mentioned by Bird, that can be operated using the rear remotes. However, keep in mind to make sure the hydro flow rate of the tractor is going to be enough for the implements you'd want to use. Remotes can be very very useful. Especially popular it the top link cylinder and right lift arm cylinder that Bird mentioned. Really helps when using things like a boxblade that need to be adjusted often for leveling etc.
John