Jake brake on or off driving on flats or small hills?

I have a Jacobs Exhaust Brake on my rig. I leave it on for local driving around town, but turn it off on the highway, especially when using the cruise control. The reason for me is, when the cruise control backs off on the throttle to adjust the speed, it will activate the exhaust brake. I will however turn it on when coming to a toll plaza or Exit ramp. Right or wrong? I don't know for sure, but that method works for me. If steep grade driving, my method may have to vary somewhat I'm sure.