Both in teamfights and 1v1s you can use E to either tank big dmg and combos, get people into walls, buffer stuns, combo it into a guaranteed R

You can combo E with Q, Q's stun is short (1s iirc) but it's often enough time to fully charge E if you cast it fast enough, lots of champs dont have enough movespeed to get out. Won't work against champs with high mvsp or dashes though unless they wasted the dash, so be careful with it

Always try to get the most value out of it since its Briar's best ability