To properly answer this question, I decided to reach out to an expert on the subject! Martin Beaumont, the founding director of the patio cleaner company Monty Miracle told me, “You can leave your wooden patio furniture outside if it has been treated. Fresh air is good for wood. Covering it could cause a build-up of damp and mold. But it will be affected by the elements: sunlight, rain, and frost will all take their toll. So if you want your wooden furniture to last, then you need to clean it thoroughly on a regular basis, and once dry, add a layer of sealant.”
Of course, I get that most people don’t have a huge amount of time on their hands, but you don’t need to cancel your plans just to clean your outdoor furniture. According to Beaumont, you only really need to do this twice a year at most. “Think about maintaining it rather than repairing it. Avoid jet washes which can be very harsh on the wood, stripping the top layer, and instead use a cleaner.  Once rinsed and dried, add a layer of sealant. It will last a lot longer and look a lot better!” There ya have it, people!