Haha yes it does look a bit lonely. Case size is a matter of preference so long as it's big enough. Too big is generally only an issue if you're limited on space where you plan to put your case such as under a desk, on a particular shelf etc. Bigger cases might need slightly stronger fans to get air flowing all the way through the case but don't suffer as much from rapid heat build up due to being cramped.
Like Gam3r01 mentioned, some cases can present a problem of cables reaching. Especially if they have a bottom mounted power supply with a long reach to the top combined with cable routing where the cpu power cable has to go through to the back of the motherboard tray, up the back to the top of the case, back through the motherboard...