"Along with motion toward the fifth (V), IV [the subdominant] appears as a corrective, depriving V (the dominant) of its independence and pointing it back in the direction of its origin [I]." In the key of C, IV provides the note F♮ and eliminates the possibility of G major, which requires F♯. The progression is also often used at the end of works and sections.
^ abcdefghJonas, Oswald (1982). Introduction to the Theory of Heinrich Schenker (1934: Das Wesen des musikalischen Kunstwerks: Eine Einführung in Die Lehre Heinrich Schenkers), p.23. Trans. John Rothgeb. ISBN 0-582-28227-6.