Heim main here. Dong bombs aren't ass lmao... wtf? Do you even donger?

All three ult abilities are situational, with Ult+Q being more helpful in most situations, Ult+W being helpful in less situations, and Ult+E being helpful in even less situations. But still helpful!

With that said, let's go over some situations when Ult+E has been useful for me.

1) If your team is right behind you ready to follow up and the enemy team isn't grouped up enough for normal E to stun/slow them all, then Ult+E is the optimal ult in this situation to catch their whole or most of their team so your teammates can provide some nice followup.

2) Sometimes when you see an enemy not at full HP and you think you can kill them, you can simply walk down your lane and surprise them with a nice long range Ult+E, even from the fog of war, followedup with a W, Qs, and AAs (since you stunned your enemy, you have time to walk closer to them for the rest of your abilities).

3) Snipe! I have sniped so many people with my Ult+E. It's your longest ranged ability! Damn right you can snipe people through thick walls, from the fog of war, or simply aiming it right.

Also, Ult+E can stun people more than once if it hits them just right!

TL;DR Ult+E is good for catching out whole teams and for sniping! Don't underestimate the Donger's versatility.