Beating mobs to 5% life?

[KittyPr]

i often leave the mobs at 5-10% life
why ? because i'm summoner and my dots do the rest of the job lol

[Rochetm]

Because that last bit of HP is often a waste of whatever we are about to use next... that and dots will normally finish stuff off. Mnk, Drg and Brd can all throw out a quick aoe if there are several targets to finish off anything low on hp. Summoners are rarely focusing anything other than bosses and if they are you should ask that they stop.

[PArcher]

I will do this occasionally (though not at 5%, usually a bit more) as a DRG, especially when running in a full-relic group. I'll often apply my DoTs and one Thrust combo and suddenly the enemy is at 15-25% hp, not enough to get another combo off (often in a good group I'll only be able to get a True Thrust off before it dies at this point), so I'll switch targets and start applying combos to it. Usually this also involves an assumption that the other DPS will finish the mob off.

There have been some hilarious situations where both DPS (usually double DRG AKs, though it also happens with DRG/BLM there) switch targets at pretty much the same time and DoTs aren't enough to kill it. Everyone just stares at this almost-dead mob for a few seconds after everything else is dead wondering why its still alive, then laughs as it gets nuked.

[Ysarel]

If people are switching early and not going back to kill it if needed, that's bad. But switching early is a good idea, especially with all the DoTs and debuffs you have to maintain in this game. For some classes it might take a few GCDs before they're at a good point in their rotation to switch back, and every job has some incentive to switch before the mob dies.

[Arkista]

Dots........... But on MNK I will do this if It means I will be wasting Opo form, means I can get DK up on the next mob.

[Aetheryn]

As a BLM it's pretty simple - the GCD, along with the cast time of every spell I have that actually does respectable damage, is too long to warrant another cast when the mob could/should/and probably will die before my cast finishes. If the game would actually stop my cast when my target dies, instead of letting me stand there continuing to cast on nothing like an idiot, I'd be more inclined to finish off a mob at very low health. Switching to the next mob is simply more efficient. And in the event that DoT's, or rest of the party, didn't finish the mob off either, I'll throw a Scathe on it and hope the extra damage proc'd.

Also, as others have mentioned, a lot of DPS classes have somewhat rigid rotations. Sometimes you don't want to hit the almost dead mob with a big damage skill, but that's where you're at in your rotation. So you might switch to the next mob at full(er) health at this point. There are a lot of reasons, and people have been doing it since forever.