Companies have also learned to work cooperatively to achieve their strategic IP goals by leveraging defensive patent pools, covenants not to sue, and creative cross-licensing models.

FORBES: State of the Intellectual Property (IP) Union

This sounds like Facebook is planning on using the patent as a defensive move, to protect against lawsuits from other patent-holders.

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Such a patent was usually intended to be used as a defensive shield and only asserted (or threatened to be asserted) if another party made the first move.

FORBES: Old Model: Patents Protect Products. New Model: Patents Themselves Are Products

Its patent library would presumably allow it to play an offensive as well as a defensive game.

FORBES: Patent Stalker