Placeholders

World of Warcraft is a relatively fast game, where you hunt the same monster type rarely for more than one hour. That brings a lot more variety into the game than in Everquest, where you would kill the same monster type for many hours, if not days. But on the downside I noticed that WoW players know a lot less of how spawns work than was common knowledge in EQ. I was quite surprised when I recently mentioned placeholders in a WoW conversation, and nobody knew what it was. So I'll explain it here:

World of Warcraft, like most other MMORPG, works with spawn points that are connected to the spawned monsters. That means that if you kill a particular mob, a couple of minutes later a new mob will appear at the same initial location (although it might then wander away from that initial spot). If you don't kill the monster from that spawn point, no new monster spawns. Thus if nobody hunted in an area for some time, the number of monsters there will be equal to the number of spawn points, preventing massive monster overpopulation.

Some spawn points always spawn the same type of monster. Other spawn points have a list of several different possible monsters that can spawn from it. Now imagine you are in the cave in the Western Plaguelands where the nature elementals drop the Greater Nature Protection potion recipe. You will see both elementals and slimes in that cave. By stealth you manage to kill only the elementals, but never the slimes. After having done so for a while you will notice more and more slimes, and less and less elementals. Because every elemental you kill is linked to a spawn point, where either an elemental or a slime can spawn. And if you selectively kill all the elementals, sooner or later all spawn points are blocked by a slime. In this case the slime is a placeholder for an elemental. You need to kill the slime to unblock the place it holds on the spawn point, and have a chance for an elemental to respawn.

That used to be very important in Everquest, because some spawn points had a low chance of spawning a rare monster, with better treasure. So if you wanted that specific treasure, you needed to kill the placeholder on that spawn point until the rare monster spawned there. There are some rare spawns in WoW, but I don't know of people camping those spots.

The important thing is that knowing about placeholders teaches you that you shouldn't hunt too selectively. If the population of your target monster is low in the area where it should normally be, maybe somebody just hunted them and didn't kill the placeholders. For example the first step of the tier 0.5 quest has you hunting spiders and scorpions in Silithus. When lots of people do that, it gets hard to find any spiders and scorpions, but there are a lot of sand worms around. Instead of running around endlessly searching for a scorpion or spider, a much better tactic is to start killing sand worm placeholders in some area, thus making it more likely that a scorpion or spider will respawn near you.

There are lots of placeholders in World of Warcraft, not only for monsters. The thing that annoys me most is people not looting treasure chests completely. Chests often have some better and some junk stuff in it, and people not knowing how spawns work (or not caring) only take the good stuff out and leave the junk in. Then the treasure chest doesn't despawn, thus the spawn for the next treasure is blocked. I think things in WoW can despawn on their own, but on a very slow timer.

A bit less obvious is spawn points for resources, like herbs. But sometimes I noticed that for example in Azshara there were lots of less valuable Sungrass, while the more valuable Dreamfoil, Golden Sansam, or Mountain Silversage were all gone. In that case I always harvest the less valuable stuff, because it can be a placeholder for the more valuable stuff I want. With resources the respawn timer is long, so it takes more patience to profit from removing the placeholders, but it is still worth it.