How does senatorial courtesy affect the appointment of federal judges?

Senatorial courtesy is an unwritten political custom (or constitutional convention) in the United States whereby the president consults the senior U.S. Senator of his political party of a given state before nominating any person to a federal vacancy within that Senator's state.[1] It is strictly observed in connection with the appointments of federal district court judges, U.S. attorneys, and federal marshals. Except in rare cases, the courtesy is typically not extended by the president to a state's senators when the president and senators of said state are of different political parties.