The group had recorded the songs in a five-day stretch during February of the same year. It was to be the last album to feature founding member Miroslav Vitous as the primary bassist.
Zawinul began to assert greater control of the band, steering it away from the collective improvisation that marked its live performances toward more structured compositions emphasizing funk and groove. This was exemplified by the album's two dominant tracks, "Boogie Woogie Waltz" and "125th Street Congress," as well as the closer, "Non-Stop Home." Other tracks were reminiscent of Weather Report's previous albums. Sweetnighter is considered to be the most stylistically transitional release by the band as it bridged the gap between the more open, improvisational earlier style to a more compositionally structured format. Also, the more prominent use of electric bass is evident here. Zawinul had taken the decision to add some funky beats in the band's sounds, so he recruited drummer Herschel Dwellingham and percussionist Muruga Booker to play on the album. Andrew White was hired to play the English horn, but also handled the bass for three tracks of the album.
Reviewing in Christgau's Record Guide: Rock Albums of the Seventies (1981), Robert Christgau wrote: "Ask yourself: What kind of a jazz (or rock) (or jazz-rock) group would conceive its sonar identity around electric keyboards and soprano sax? A pretty dinky (not dunky) one, right? So while I'm pleased that they're going for a drum groove a little solider than anything Dom Um Romao can move and shake, I'm not surprised that they get it only—just barely, in fact—on '125th Street congress.' And that 'Boogie Woogie Waltz' is fatally cute, ace improvisations and all."
(en.wikipedia.org/wiki/Sweetnighter)