Many have changed the name of this from "disconnect" to "battery isolator" which, to me at least, is more descriptive of what it does. It doesn't completely disconnect the battery, but it does isolate it from most of the coach, including the converter/charger.
There are things, such as the CO detector and Propane detector, that are not wired through this switch, so they tend to be parasitic draws even when the key is off and removed.
I added a true disconnect switch to my batteries on the negative post to prevent this drain. Here's the one I used...
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1