If an entity using an animation that causes it to emit a particle with an emitter lifetime of 1, the emitter does not despawn upon the entity's despawn (whether it be despawn by events or post-death).

While the particles do not appear, the emitter is still active, leading to an invisible source of lag. If this occurs a lot in one area, it leads undetectable lag spike that can only be prevented by restarting the world (as closing worlds gets rid of all particles).