Most visual effects would be impossible without them. Animators rely on them for complex scenes that would be ludicrously time-consuming to keyframe. You can even use them to create fur, feathers or grass. Yet particles remain one of the most under-exploited tools in 3D software.
The problem is that the enormous versatility of particle systems is also their undoing. Faced with a bewildering array of controls, drop-downs and parameters, many artists simply opt for the default settings. The result is either one of the tell-tale signs of CG animation - sparks that seem to move in slow motion, synthetic-looking flames, and smoke that fails to respond to the prevailing wind - or flames that take days to render. Yet all that is often needed to transform such problem systems into flexible, fast-rendering effects is a few simple parameter tweaks.
