I use demolisher cannons for anti infantry mostly.
Though I did scatter from a massive squad of necrons into a monolith, immobilising it. Was fun.
Large template, AP2, strength 10, that's a "Kill every heavily armoured person in the building" weapon. Seems a waste to use it on vehicles unless they're the only targets.
Battlecannons also serve the same purpose, but I believe they're AP3, and thus can't mince Terminators. However they usually make up for it by being much longer ranged.