Equipment. Yeah it's the temp swings that do it.Do you mean equipment sweating or people? Cause in my old unheated shop in NC my anvil would sweat in the cooler months when there would be 30* temp swings. Some of that has to do with the humidity but I'd rather not have large temp swings in my shop in general. It's hard on things and promotes rust.
Everything in my garage stays moisture free until you have increasing daytime temps at which point opening the doors results in every heavy piece of metal sweating from the warm air (which is why my machine shop is the basement). A well insulated shop will do this a lot more days out of the year. If you have a huge shop and are just opening a small garage door then you might get away with it but every time you change out a lot of the air in the shop and the stuff in the shop is colder than the air coming in it will sweat. You can probably get away with it if you air-condition but that's a lot of money up front and a lot of recurring cost.