The answer is simple. If you are well known and popular, definitely yes. If not, you can only benefit from it if you do not pay them (too much).
It will definitely not be bad for you as a player. Nevertheless, in our opinion only the true top players could really monetize their social media presence. In such case a social media agency could become a very useful partner.
Over the last five or so years, the number of agencies that manage social media for footballers has grown exponentially. Often it concerns smaller companies with a couple of employees at most who take care of the communication on Twitter, Facebook and other social media on behalf of the footballer. However, the range of services is not restricted to social media but often comprises all the player’s communication to the outside world. Building a website, reaching commercial deals or even contacts with the press are also these agencies’ responsibility.