[X] Rolling Thunder is an incredibly powerful initiation tool for your team. Communication and timing are key factors to using this ability successfully, because of how perfectly it can set up your team for some easy picks.
[Q] Flashpoint must be casted through walls, objects, floors, etc. and can be done so from range.
[C] Aftershock is typically used to zone enemy players, clear space for your team, and on maps with a high pick % for Killjoy is often used to break Killjoy's Ultimate ability.
When [X] Rolling Thunder is capitalized on well by you and your team, it creates an overwhelming force that can singlehandedly decide the outcome of the round. Enemy players often save their Ultimates just to be able to counter it!