The "iii-VI-ii-V-I" (3-6-2-5-1) chord progression is, and has been, one of the most common harmonic devices found across virtually every stylistic genre of Western music.

As with its close cousin, the I-VI-ii-V-I, it's root movement is based on the Cycle (or Circle) of 5ths, creating a logical sounding (if sometimes cliched), harmonically satisfying resolution in the ears of the listener - meeting anticipation and expectation.

Pick a tune from the "Great American Songbook" or almost any Jazz standard and you'd be hard pressed to find one that's completely devoid of this harmonic cadence. It has served as one of the harmonic foundations for improvisers for more than a century.

The interval of a Perfect 4th (P4th) needs no introduction. As an inverted Perfect 5th, it plays a role in the formation of the Major Scale matrix through the Cycle of 5ths.