Particles can be aligned in a variety of ways to enhance the composition of an effect. The basic alignment used in most particles is camera alignment. In camera alignment, the particle is always facing the camera straight on. Particles can also be aligned to the world axis or an object axis. An example of this is a round glow particle that lays flat on the ground to fake lighting from a nearby explosion effect, which is a cheap way to achieve convincing results.
A third form of alignment is velocity alignment. In velocity alignment, one edge of the particle aims toward the direction it is traveling. This technique can be very useful when creating directional sparks outward from a bullet impact point, for example.
By varying the types of alignment used, one can make particle effects feel as if they have more volume. Flat, ground-aligned particles blended with camera-aligned particles can help to hide camera-aligned particles clipping into the ground. Velocity-aligned particles can help add volume to the shape of camera-aligned particles as well.