Unfortunately this is an old post, but I do hope that you’re able to see this response, or that others may come across my answer to your dilemma. The cost of the second seat is refunded to you upon arrival at your destination. Purchasing a second seat in advance allows Southwest to properly seat their flights accordingly. If a person of size only purchases one seat, and the flight is completely full, and the plus sized flyer is of such a size that the second seat is actually needed for them, then it is probable that the person that purchased their own ticket and would have been sitting in that seat will instead be moved to a different flight, causing them to possibly miss whatever event they are attending. Since the second ticket is refunded, it is common courtesy to purchase it in advance so that every customer can be served
