There is one issue with leaving it plugged in. If you lose AC power ( power outage, cord gets unplugged), you now have a load on the batteries. If you hook up to a good maintainer (that imparts no load when the AC is unplugged) and turn the house switch to off, this is a non issue. You don't have to ask how I came to this knowledge.
I have a permanently mounted 10 amp battery charger/maintainer in my battery bay. It's also my backup 12 volt supply in case of a converter failure.