We pretty much use it all the time even at MTOW. Remove the derate in the climb if necessary otherwise just leave it managed to sort itself out if no level restrictions. DCLB will use slightly more fuel than just using normal climb power however there are savings to be had in engine wear. I guess our company is happy to burn a bit more to save the engine life. No figures on how much extra it burns but in the grand scheme of things it would be minimal