To give you an idea of the situation where you'll want multiple rez spells, here's what happens in Tower of Despair part 2, when fighting Nytharios the Shadowmaster.
Most of the group will be meleeing a boss that isn't very dangerous (one cleric casting Maximzed Mass Cure Critical wounds every cooldown will be overhealing). However, at various times extraordinarily deadly Shadowfiends are spawned by the boss. They have no noticeable melee damage, but everyone within a Haste radius of them takes about 240 cold damage every two seconds and that's per Shadowfiend.
Frequently someone will take two Shadowfiend damage pulses without being healed in between (420 damage after resists, assuming no Fire Shield and an already-expired Protection) and this kills many players. Three pulses without healing kills almost anyone. However, this often happens just before the Shadowfiend is brought under control and taken away from the boss.
It's important to get players raised fast, however, as the Fiends keep coming (they despawn at certain percentages of Nytharios's health, and are extremely difficult to kill any other way).
You often get a situation where as many as eight raid members are dead, but the crisis is over. In this situation it's critical to get everyone up and quickly. A cleric should cycle three quickened raise spells (maybe scrolls too), a FvS should cycle all they have, and they are much more useful to the raid if they have two (or three, but that's probably too much to ask of a FvS).
Epic Raiyum sometimes has multiple deaths, but they are more avoidable and can be attributed to a caster not getting aggro of Dread Hex wraiths quickly enough, or perhaps the caster getting interrupted when drinking a Remove Curse potion.