Why would hanging them from the ceiling not clear space from the floor?
Well, it does, but unless we’re talking about a particularly high-rise shed it doesn’t clear a very tall region of space so there’s a limit to what use you can make of it. And if you do make use of it then you generally need to move the stuff out of the way when you want to get the bike down.
Personally I’d just use one hook attached to either the ceiling or the wall and store the bike vertically, hung from one wheel. YMMV. Depends on your shed/garage layout: hanging mine vertically leaves enough space to walk past, where having them hung horizontally from the ceiling wouldn’t… I’d have to use the space underneath to crawl through 🙂