I’ve shared our journey a couple of times.
We did a major downsize from 3,500 sq ft to 935 sq ft when we moved to Florida. Had a living estate sale and got rid of most of our belongings. Our ds was still in college, and I did have him go through his stuff when he was home for Christmas before the big downsize. However, I told him not to feel compelled to get rid of anything as we knew we would have a storage unit when we first got to Florida. Initially it was a 10 x 10. We had Christmas decor, sentimental items, and ds’s things. Not sure what else, really. It was a larger space than we needed, but that made everything quite accessible. When ds visited for a spring break we went through the storage unit, and he got rid of a lot, often asking aloud, “Why did I keep this?” That enabled us to move down to a 5 x 5, which helped because the rate had crept up on the 10 x 10. Eventually the rate on the 5 x 5 became higher than the initial rate on the 10 x 10. They were very clear about the intention of their units - this is supposed to be temporary storage, and your rates will go up. We purged some more and invested in some efficient shelving and storage containers and got everything to fit in the on-site storage closet that each condo had. It was probably only 3 x 4 but pretty tall.
We then moved to a 1,600 sq ft condo that did not have an on-side storage closet. We had a small storage container in the condo garage. With more square footage in the condo, everything worked.
We have now moved back to the state we left Florida for. We are up to 1,900 sq ft and back to having a two-car garage (something we never had while in Florida). There is entirely too much storage in this townhouse for us. I will never fill it up. I will work had to make sure I don’t. I will not burden my kid with a bunch of crapola.
I know people who have storage units solely for the purpose of storing their Christmas decor. These people put up multiple trees, have elaborate tabletop decor, and Christmas china. People should have and do what they want, but I cannot imagine spending that kind of money and time on that. I am no Scrooge, but one tree is enough for me.
My mil had a friend who had a storage unit holding his mother’s belongings for over ten years in his hometown. I think he kept precious little when he finally went through it. So much wasted money.
IMO, outside storage units should be used as a temporary mechanism when necessary. If your stuff won’t fit in your house, get a bigger house or get rid of the stuff.
Edit to add - our garage has two, “soccer chairs,” and some shoes. Being in a townhouse means no lawn/bed maintenance for us which definitely helps with keeping our garage virtually empty other than our cars.