How to make enemies bang doors

[Cranky Old Man]

do you have to preload a particle entity?

Preloading is recommended when you haven't already placed the particle system in the map. If it is in the map, then it'll get loaded with the map.

If it's in the map, you mean like if it's permanently active and not summoned by something like a scripted area?
I've preloaded all my particle effects and sounds, but I don't notice the slightest difference. Is it only noticable on slow computers? How slow are we talking?