I wanted to be able to make a light flash forever without having to enter a whole bunch of key frames in the dope sheet. Turns out using the graph editor you can add a variety of procedural effects.
Later on I needed to add a bit of secondary motion to a robot helicopter. Turns out you can also use the graph editor to do this. Add start and end keyframes and then apply a function (sin curve) to get a nice little wobble. Super handy and very easy to tune. The Blender community and YouTube are amazing resources :-)