Teach me when to use Onslaught.

[Chrono_Rising]

I'd disagree. So many other melee gap closers do not consume any resources. Look at DRK's Plunge. Zero resource and its 200 potency, where at Onslaught costs BG and is a small 100 potency. Far from being the best desgined gap closer.

That said, I am not denying that it is useful in many scenarios.

Though it is half the potency it is also half the cooldown and has a longer range. The 5 extra distance is really nice for getting back to the boss in a lot of fights. Plus oGCD enmity generation. There are definitely downsides to both tank gap closers.