The 4 sits where the 3rd wants to be, then falls home. Zero accidentals, instant motion on a chord you're already holding. The single cheapest way to make a strummed bar feel alive instead of parked.
movesthe 4 leans down onto the 3 — one finger, usually one fretsolo·singnothing changed in the key — target the 3 as the sus releaseson recordPinball Wizard — The Who (the sus4 pump) · Free Fallin' — Tom Petty (the chime)try itEvery long tonic bar in your song: hang the sus4 for beats 1–2, release on 3.