On a normal controller, you may have just as many switches as on the InterLink DX, but they don't do anything until you program a purpose for them. In RealFlight, they can all potentially have a function, but it does depend on each individual model to implement those functions and do it in a manner consistent with other RealFlight models.
I'm kind of surprised that there isn't a direct answer to this question in the RealFlight manual, but maybe it's because the switch functions can vary by model.
Here are some highlights to help get started that seem to be common across models if they support the given function.
Switch A - Move retractable landing gear up or down, or else activate a smoke trail on some models
Switch B - Change flight modes on models that implement Horizon's SAFE trainer or SAFE Select technology
Switch C - Elevator Dual Rates (also called Low Rates)
Switch D - Flaps
Switch F - Aileron Dual Rates
Switch G - Rudder Dual Rates
Switch H - Throttle Hold (all helicopters in RF are designed to keep the motor off when Throttle Hold is turned on)
Button I (on top) - Panic Mode, if equipped (only on beginner-style aircraft), or also Thrust Reverse (on planes equipped with that function)
Some models have all of the Dual Rates on one switch (Switch C), but RF is designed to allow the three to be controlled separately if the model is set up that way.