Motorhomes differ in what exactly the disconnect switch connects and disconnects. There are typically a couple of common setups when you have a converter (rather than an inverter/charger).
One setup is that the converter and the house circuits are on one side of the disconnect, and the battery bank on the other side. In that setup, with the RV plugged in and the batteries disconnected, the house circuits will generally have power (from the converter) but the battery will not be charging and will eventually self-discharge. I think this is the most common arrangement.
Another setup has the converter and the batteries on one side of the switch and the house circuits on the other. In that case, the converter will keep the batteries charged when disconnected and on shore power but the house circuits will not be active.
If you have an inverter (at least one of any size), it generally is connected on the battery side of the disconnect so the disconnect doesn't need to carry the heavy inverter current. If you have solar, that should be on the battery side as well since many solar controllers do not like having the panels connected but no battery connected.
In general, there is no need to use the disconnect when plugged into shore power. The disconnect is mainly of use when in storage with no external power or when working on the 12V system...and in the first case, it's often of only limited use since frequently there are still some small loads present even with the batteries disconnected.
