I not only leave our plugged in, but I also set the thermostat to 80F. This way the A/C cycles, keeping the humidity out of the rig. I've been doing this practice since 1994 on our last two RVs. Florida humidity can cause mildew issues in RVs that are not kept dry inside.
Totally agree with other comments regarding good battery chargers. A good charger will also equalize the cells periodically, preventing water/acid stratification inside the battery. That will kill batteries. I've had batteries die early from living on a trickle charger. Doesn't gently bubble the solution to mix it adequately.