Voting. Only U.S. citizens can vote in federal elections
U.S Citizens typically have a much faster and easier process to sponsor Family members for U.S status.
Traveling with a U.S. passport.
Becoming eligible for federal jobs.
Becoming an elected official.
Showing your patriotism.
Reducing Immigration/attorney fees as are required with renewing Green Cards.
Never lose your U.S Citizen status. A Green Card holder can lose his or her LPR status in certain circumstances, such as staying outside the U.S too long.