I've always looked at it as being the same as keeping a battery on trickle-charge over the winter to keep it topped. Some say that's good.

It's always on all summer, and stays at or near 100% unless we have a cloudy day (or three). The refrigerator is on in summer. It can run down if we have extended overcast but it has a low-voltage disconnect (on the fridge circuit) at 11.9v so the batteries won't be damaged.