There seems to be a common fixation on objects "modeling the real world" with the counter argument for classes being that they don't model the real world. True, there isn't a physical chair class in real life(philosophically, there aren't even chairs), but there is a common abstract idea of what would describe the function and attributes of a chair. Granted, it differs a little from person to person, but objects them…
Inform7, in its beautifully literal (not to say literate) way, captures this very simply with the way it defines classes (what it calls 'kinds'):
A chair is a kind of thing. A chair can be comfy or hard.
Your favorite armchair is a comfy chair in the living room.
Other languages might use other techniques to capture 'chairness' without having to start off by describing the class of 'chair'. Maybe you define the protocols chairs support (sittability?), or you just rely on dynamic typing and write code that just assumes whatever is passed to it is a chair and can be sat upon, without the code ever needing to be able to divine an object's chairness. That's useful! you can sit on things that aren't chairs, after all. If you can only build objects from classes, though, you can get yourself into the situation where you find yourself having to find a way to compose a 'chair' instance into your 'bed' class so you can allow someone to sit on the bed without having to copy paste code.