Some real good comments here !
Cover or no cover is truly a "it depends" situation. That would also apply to cover material and design.
How is the boat stored ?
What weather conditions are involved ?
How bad is the UV ?
How much are you covering ?
Lake Ontario in an area that routinely sees over 100 inches of snow each year. If it was located in a drier less exposed area I might think differently about the cover, on the other hand, the ability to work inside the boat in most any weather is a real plus.
In those conditions a cover really makes sense.
Material and frame would need to handle that snow load.
I would love the ability to work on the boat in winter.
Here on the prairies we don't get much snow, and a cover would be useless to work under unless you had a heater.
Shore power is off all winter so that would be propane or kerosene.
For example Its been below -30 for the last couple weeks.
Wind blows most of the dry snow off the deck. Temperature traditionally doesn't freeze/thaw much at all. Lately, summer and winter are like flipping a switch. The cockpit drains are the big risk, but most of us empty the cockpit before it melts in spring.
Deck penetrations can be a problem, but they are a problem in summer too. To me, it's the one of the first tasks when you get a used boat... Pot every hole and rebed. Problem solved long term.
I've been in boat yards where the wind has blown over boats with their masts up
Because we don't have open Travel Lifts in the yards I've used, the mast comes down every year.
No stands here. all are cradles or trailers.
Biggest boat is currently 35ft.
Most are trailer launched with a caterpillar. For this reason, most boats are stored mast up. The ones that do take their mast down are usually launched by our "closed" travel lift like
@dlochner mentions.
We have some serious blizzards. Based on what I can find online, the record speed is 107kmh/66mph in January 2016.We had plow winds one summer that tore up trees, but that was summer. The "old timers" here tell me they haven't seen a boat topple in storage.
In the time I have had storage there, I see at least 1 cover that failed it's attachment, beating the crap out of their boats, every spring. Like anything else that's a design or maintenance issue but it's one more thing to worry about.
If I ever have spare time, I may make a cover, for the cabin top, mainly to protect the wood from UV, but in this climate area I won't lose sleep over it.
Once you get the hang of taking them down, it's not that big a deal and it forces you to retune the mast every spring which is probably a good thing
Agreed. I need to set a maintenance schedule for occasional mast removal.
I dodged a bullet with this boat. It was stored mast down for most of its life, due to crane method.
Previous owners put spray foam in the keel stepped mast, without a drain outlet. Likely to try prevent water in the bilge.

Had I not found it before I stepped the mast, it would likely have damaged it when the water froze.
Is a mast up cover problematic compared to mast down ? Other than cost and setup time.