All third-party integration with WordPress.com occurs via a WordPress.com application (an application defined at developer.wordpress.com), and every application is owned by one and only one WordPress.com profile. You could either develop and code your own service to operate your application, or you could use an existing service to act as your agent.
The SocialOomph service is the agent that acts as the operator of your WordPress.com application.
This arrangement means you own the WordPress.com application that posts to your WordPress.com properties, and you use SocialOomph as the software engine to do that posting for you.
It holds the following benefits: