Whether using the disconnect is a problem or not... depends a lot on the converter. Years ago I tried powering a car stereo off a battery charger. Did not work very well as the power from the charger was not very clean: it had the A/C 60 cycle humps in it. This caused a hum through the stereo which was eliminated by having a battery in the circuit.
Electronic stuff has advanced a lot since then but I could still see the battery providing the ultimate power filtering in a converter system. I could also see a converter that was trying to be smart only powering up the 12V side if a basic voltage was present.
That said, simple converters may put out a higher voltage than a fully charged battery needs since they also try and charge the battery (which *does* require the higher voltage). And in this case disconnecting the battery would help.
2015 Rockwood 2604WS (sold as 2016)
2014 Ford F-150 Ecoboost