The only real benefit I know of is if you have two distinct writing styles or genres and want to keep your audiences separate.
That said, some hubbers open second accounts for the reason rclinton5280 mentioned - to have a cover to hide behind when writing B.S. However, unless you can write in a *totally* different voice, this only works for a little while. Otherwise followers of your original account will recognize your style, and then what's the point?
Last on the list are hubbers who open a second account for the sole purpose of spamming and slamming other hubbers in the forums. Such accounts are called "sock puppets" and usually detected early on (and even banned) because the perp doesn't bother to write any hubs under that account.
I DO have two distinct writing styles and genres, so I have an account at HP for one and a blog for the other. Totally different group of followers that way, and *I* don't get confused about who I'm writing for! ;D