Knowing what your competitors are doing arms you with information you can use to make your marketing campaign on social media even more successful. Just like your rivals Facebook page, follow them on Twitter, etc. Having done that it will be very easy to know what your rivals are doing right, what isn't working for them and so on. Copy what they are doing right and having learned from mistakes they make, obviously you won't do the same things they did. It could give you a competitive edge.