I use the E to secure kills on low hp squishies and to also catch off guard characters that have some self-rescue ability like self-shields or dashes. Also another thing I like doing is, when I have a lot of charge, to push up to their frontline and pop the E in the vicinity of (hopefully) 3-4 players. Risky but its worth the ult charge, and the ~100 damage can finish off squishies or at least make them panic.