We didn't have one on our Elkridge, and added one.
We park our unit for 1-2 weeks during the season (sometimes longer). We flip to 'disconnected' anytime the unit is parked at storage. The batteries stay nice and charged that way - even after being in storage all winter (Dec-May/Jun), we have good charge in the batteries when they've sat completely disconnected. On our old system, without a disconnect, the CO monitor and other small uses would drain the battery over a few weeks of idle sitting... when we had our old camper parked out front, it never failed that the "low-battery" alarm on the CO monitor would go off at 3am and wake up the neighborhood.
I wouldn't be without a battery disconnect!
Glad you found yours!