From glyph (in a particularly snarky mood):

"""
P.S.: I realize that this isn't really within the scope of this message, but as I was reviewing Future's documentation while writing it, I realized what Future.running() does.  Wow.  What a completely pointless bug magnet.  Why does this method even exist?  It seems like the only possible use would be to introduce look-before-you-leap bugs into concurrent code, like 'if not my_future.running(): my_future.cancel()'.  If it were for tracking the state of long-running Future operations for UI purposes or something, then 'my_future.add_start_callback(callback)' would be a much more useful interface, which at least has a hope of being used correctly.  Independently of the rest of stuff in this message, it would be great if that could be deprecated and removed.
"""

Despite the snarkiness, he does have a point.  Perhaps it was copied mindlessly from Java?