I would say a very light coating. Centrifugal force would throw it onto the disc and friction surfaces if you use too much and you don't want lube there.
Yep, a very light brushing of the lube on the splines is all you want to use, but it is a good thing.
It helps to make sure your clutch releases like it should, because the clutch disc needs to move forward and back slightly on the splines, and if it doesn't it can cause the disc to drag against the pressure plate.