I find the rear ABS very useful in emergency stops. The front not as much. The rear abs allows me to focus on maximising my front brake potential w/o trying to focus on the rear. When I practice emergency stops, my front may "click" just a time or three. I press the back and if it starts abs'ing, I don't really worry about it. If the front abs's, I ease off a tiny bit.
Off road, for gravel at high speeds, it's very nice, you can give the front a few good squeezes to find out where your traction limit is and adjust your speed accordingly. When going down steep, steep inclines, it scares me, but you can always shut down the engine and use the clutch as your rear brake and waddle on down.