for summoned creatures, being up to 29.9 sec without the buffs is... debatable?
Most permanent global buffs are for survivability.
Does it suck to be 29 sec without buffs, when you only live 30 sec? yes. Does it really matter when you die of "old age" anyways without the buffs? Ehh...
As for long lived/permanent summons: here the up to 30 sec rarely has much impact. What is summoned into the fight isn't expected to survive anyways and what is called outside generally lives some time before it sees combat. (I exclude PvP, because [nearly] nobody runs permanent global buffs there)
Would i prefer an instant application, or one every few seconds? Sure. But at which point can that cause server lag? As for 30 sec: i wasn't going to go through all potential effects. But everything with a tick-rate (correct me if i am wrong) is 1, 2, 3, 4, 5 or 10 seconds. With 30 being the easiest multiplier of them all, so no ticks will be missed due reapplying.
Again, all summons.
Corsair bandits, Satanel spawns, Deepfang