The major importance of the Watergate scandal in the short term was that it caused the resignation of President Nixon. This was the only time that an American President has ever had to leave office.
In the long term, the importance of the scandal was much greater. It has had at least two major impacts. First, it has reduced the trust that Americans have for their government. It has made us much more suspicious of government and has helped lead to our current negative attitudes towards government. Second, it helped to make the political atmosphere much more partisan. Each party is always trying to catch the other in scandals that it can use to harass the other party and try to prevent it from accomplishing its political agenda.