i am new disc player and priest player as a whole and i wanted to know in which circumstances dispel magic is used in raids or dungeons .
Dispel Magic is used to remove buffs from your opponents. Dispellable buffs are highlighted on your default target frame, whenever you see it, you can purge it.
In the current M+ dungeon pool, the most important dispel is in Necrotic Wake, Nar’zudah - the miniboss after the first boss before the bridge, he casts Dark Shroud buff on himself that makes him immune to physical damage and pulses shadow damage to the group, it must be cleared asap.
In Dawnbreaker, there are rogue type enemies who cast Darkblade on themselves - increasing their damage - that can be dispelled.
In Tirna Scithe, mobs in the maze can cast a HoT on themselves.
In Siege of Boralus, the horse-riding guards cast a damage reduction on mobs around them.
There are some other but they’re not that important, you will see them as you play.
I have no idea what the raid situation is.