Since particles are emitted each frame, regular 'bands' of particles may be generated.
This is especially noticeable when the emitter itself is animated.
Sub-frame emission helps to overcome this.
Normally you should leave this enabled but, if you need to turn it off, uncheck this box.
If this is enabled, the X-Particles control system will be ignored by the emitter.
No Question objects will be tested and no actions carried out.
Set as Rate, by default, there are six more options: Pulse, Shot, Regular, Hexagonal, Trigger, Controlled Only.
This is the default setting; particles are emitted each frame at a rate determined by the Birthrate settings.
xpEmitter_Emission_Rate_v02.mp4
Animation to demonstrate the Emission setting as Rate.
Normally, the emitter emits particles in all frames.
If you want the emitter to emit one big pulse of particles in one frame, turn on this option.
The number of particles emitted in each pulse is found in the Birthrate parameter.