On my last truck, I left it on with a cover. I would remove it each spring, clean, refinish rusty spots, and lube it.
On current truck, my hitch comes off in tow pieces which makes it a one person job to remove. I also have the factory "puck" system which allows me to latch/unlatch the hitch in little time. Much easier to remove.
Since we camp all year round, I leave it in the truck all the time. But, there are a lot of people that remove it. Some people leave it hanging on the king pin of the RV during storage and some have racks built to store it.
The case for removing it is that your bed is free for stuff you may want to haul, and it's not subjected to harsh weather and chemicals (i.e. salt) if you store it under cover or hanging on the king pin.
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Salem 29RKSS Pushing a GMC Sierra 2500HD!
Gotta go campin!