What advantage does the majority party have in congress?

As of 2010, the Democrats hold the majority in both houses of the United States Congress.

You need to be more specific and say which country you are referring to and what year or years. Please re-state the question.

as of 2007 the majority party is the democratic party

No.

For the current 111th Congress (2009-2010), the Democrats control both the House of Representatives (255-178) and the Senate (57-41-2).