The Montgomery Bus Boycott had at least three outcomes that can be seen as important.
First, and most immediately, the boycott was successful in achieving its stated goal. The boycott was successful in getting busses in Montgomery desegregated. This was not important to most people in the US, but it was important to the people of Montgomery.
Second, the boycott helped to launch what we know of as the Civil Rights Movement. This was the first sort of direct action that was undertaken on a large scale in pursuit of civil rights. Before this, the main efforts of groups like the NAACP had been focused on law suits. Now, the movement turned more towards protests of the sort that we associate with the movement.
Finally, the boycott launched the career of Dr. Martin Luther King, Jr. Before the boycott, King was not a nationally-known figure. After the boycott, he had emerged as a major leader in the civil rights community. The boycott helped to make him the face of the Civil Rights Movement.