My preference is not to leave the RV plugged in all the time. There are several reasons for this. First, many (most) factory installed converter/chargers make lousy battery maintainers for long term use. Most of them have a tendency to overcharge and boil the batteries dry. Second, if you aren't using the RV, there isn't any reason to have all of the appliances, converter, TVs, etc... powered up waiting for a lightening strike or other power surge to hit them. The next couple of reasons aren't as big a deal, but still matter to some. There is no chance of forgetting to turn off the water heater, refrigerator, etc... if there is no power to the RV. There are always "parasite" power drains, the power it takes to run the clock in the microwave, keep the TVs in standby, etc...
It is true you could eliminate many of those problems by flipping the breakers to those appliances off, but that still leaves my first and biggest reason.
I kept our most recent TT plugged in for the first year and had to replace both batteries. Yes it's my fault for not paying close enough attention and not keeping the batteries topped off. After replacing the batteries, I installed a battery cutoff switch and wired in a battery tender quick connect directly to the batteries. Now when it's in storage, I flip the battery disconnect off and plug in the battery tender.