You should use it to maintain higher uptime on bosses, some examples I can think of include prey in a5s (you keep hitting him until the very last seconds before you use elusive jump to survive the dash), single drill in a6s (elusive then spineshatter back to the boss), aoe marker in nidhogg ex after the adds phase (keep hitting until just before it drops the aoe puddle, then spineshatter back to the boss), bombs in a7s or just returning to the boss after doing jails, padlocks, adds or anything.

Basically during anything you need to move away for, you can reduce your dps loss by using elusive and spineshatter or dragonfire, and of course sometimes as an ohshit button to get out of aoe after getting animation lock from jumps.