This is useful for, for example, triggering different weather conditions. In this example I'll add different types of snow.
This VFX project was an exploration into creating realistic fire which would burn from ignition, through initial burn to a roaring flame and then eventually dying.
I wrote a Python script to convert a sequence of image files into a grid for looping, seamless animations, ready for use in Unreal Engine or similar.
As an example, say you want to spawn a blueprint actor called BP_FIRE_LOG and give it a unique ID number so that it can be referenced in the level.