The CRJ is 3-phase and I assume any others would be too.

Using 3 phases gets about three times the power out of a given size and weight of generator case. For that reason almost any industrial or weight critical gen will be 3 phase.

But except for motors, most electrical and electronic devices can only use one or two phases, so the phases are usually split off to different subsystems. An exception would be powerful electric motors, like a hydraulic pump...that would probably use all three phases.

Grid power is the same way...it is generated with three phases at a very high voltage. The voltage is stepped down along the way and only two of three phases are delivered to your house. Most circuits (lights, 120 outlets) use one phase at 120V. The second phase might only be used by large 240V appliances such as central AC, washers, and dryers. The plug for those has an extra pin for the extra phase. These devices are not actually two phase devices, they just use the higher voltage available between two phases (240 vice 120).