When you watch the Let It Be documentary, a few things stand out. One is the famous ending, in which The Beatles give their last live performance on the roof of the Apple building. Also noteworthy is the energy Billy Preston brings after several uninspired rehearsals early in the film.
Clearly, the Fab Four (plus Yoko Ono) did not enjoy making the movie, especially in the beginning. The caught-on-camera argument between Paul McCartney and George Harrison led to George walking out on the band for a stretch in January 1969.
After George agreed to return, the band moved the recording dates (originally call the Get Back sessions) to Abbey Road. In the transition, they seemed to lose interest in a few of the songs they’d started.
One of those tracks was “The Long and Winding Road,” a ballad you can see Paul playing on piano at one point in Let It Be. While it ended up being the Beatles’ last No. 1 hit in America, Paul didn’t like what the song had become prior to its release.
Source: cheatsheet.com