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Low Function - this is the "low bandwidth" enabled mode. It may send some telemetry and read some sensors, but only what is necessary. This mode would generally be used after the rocket has landed but still needs to send out occasional GPS location transmissions.
Shadow - the same as enabled but no outputs are triggered and more logging may take place. This mode would be to verify if a flight computer or a part of the software runs correctly without actually affecting a flight.
Keep in mind that not all of these modes need to be implemented for every project, they are just general suggestions to follow.