Fallback tuner is not the same as fallback receiver or client mode. Fallback tuner allows you to use the tuner from another receiver. You still need to have own bouquets and channel lists etc.
Example usages are:
when you do not have enough tuners on the current box.
Another satellite is connected to another receiver. So receiver A has 28.2 and 19.2. Receiver B has 28.2, 23.5. 39e and Terrestrial.