Simply use a duplicate layer or adjustment layer before starting your edits and then you can click the eye icon in the layers pallet.
You can click on and off to see before and after as you do more editing.
Another way would be to make a duplicate before editing and not save that copy, but there's no before and after view as such in full edit.
There is no such kind of views in Full Edit. however toggling the layers in layers panel you can check the before and after.