Rear disc is very good if your in a lot of mud or sand.
One of the other benefits is brake feel.
I am still non-power so this may change when I go hyrdoboost, but I can feel the slightest lock-up and modulate the pedal for it.
As Sandmann says, totally unnecessary, but I still love them.
By going with the BC kit it allowed me to buy the parts in stages, making it very affordable.
Oh and yes just go ahead and start collecting parts for hyrdoboost, you will not be disappointed.