Of course I have cloud storage - DB, Google Drive - even Crashplan complete backup...
For editing - the file can't be in the cloud (web only storage) - it has to be SOMEWHERE locally accessible, and it's best if it's a consistent location. I have enough data now that I'm going to need more storage, and I enjoy having access to all of it from every machine - and it'd be great if that machine wasn't my gaming rig. I'll probably end up with a small NAS or I'll convert my current computer into a small server when I rebuild. HD plugged into the router would have a similar same effect.
The big disadvantage of an HD is that I can't do other things with it. For example, a DVR/media server. I have 2 TV tuner cards (no longer used) in my old gaming rig right now. Once upon a time it was a FANTASTIC and automated TV machine - I don't think I saw or even had to FF through commercials for 2 years, and I was able to use it to "Slingbox" Saints games from New Orleans to New York. The appeal of a separate machine over an HD is for things like that - Media server...and cutting out commercials etc.
Running the TV DVR/server was a fun hobby back before grad school - and I'd like to get back into it, but this time with an independent machine running the show.