I think it was @mdboom that specifically mentioned wanting it in, and I didn't want that to delay anything given there weren't other opinions at the time, which is why it got added back in.  It's definitely less crucial with the string stuff moved to the other classes, but it still might be useful when you want to ensure the internal representation is always the same unit regardless of what `Quantity` is passed in... But that's now just syntactic sugar for ``lat=(...).to(u.whatever)``. 

@mdboom, do you still think this needs to be in there?