Watch the The I-IV Delayed Change online guitar lesson by Ravi from Guitar Lab: 30 Rock & Pop Progressions
Occasionally, a chord change will be delayed by changing the "quality" of a chord before actually advancing to a new chord. One can argue that each one is an independent chord in the progression (and that is perfectly correct), however, our ear hears the change to be comparitively subtle until we actually make a more distinctive change tonally to a chord with a new root. For example, while C, C major 7, and C dominant 7 are all different chords, our ear hears them all as some sort of C until we make a more obvious change, such as to the IV chord which is an F in the key of C. So, from the songwriter's point of view, it functions more as a way to delay the transition to the new chord. When trying to learn a song by ear, hearing this as a delayed change is helpful because it is then easier to identify the progression.
Try holding the pick loosely and strumming with a light touch to give any ballad a nice feel. Accent the chord changes while laying back on the strumming. Experiment with a light touch and bring the romantic out in you!
Examples: Something, Maybe I'm Amazed, Raindrops Keep Falling on My Head