Barack Obama is the President of the United States. Which is probably reason enough to follow him on Twitter.
However, Bynes has a somewhat bizarre relationship with POTUS. After being arrested on suspicion of DUI last year, Bynes asked the President to "fire the cop" who'd pulled her over. Alas, Obama has not yet stepped in to pardon Bynes for her crimes, though he did pardon Ronald Lee Foster in 2010 after he was put on probation and given a $20 fine for the mutilation of coins.