This path is where OS X saves previous Versions of the model. This feature was introduced in OS X 10.7 (Lion) and Rhino for Mac makes use of it. It sounds like OS X is not deleting the older files appropriately. How large are the 3dm files you are working with?
You can completely turn off Versions and Autosave for just Rhino, but I’d be curious to figure out what this problem actually is.