What's the benefit of a harmony hub?

Looking at used harmony remotes online, the fact that several models come with the hub, several don't and there are some which look the same but are called something different and some come with the hub and some don't really messes with my head.

So: is there a real benefit to going with a hub and a remote? Are there remotes which work only with a hub and with nothing else? Or are all hub-enabled remotes also standard ir remotes? Should I seek out a hubbed remote such as the ultimate one or the elite, or is something like the one or the touch good enough?