It's generally pointless to talk about any of the songs from Tonight's The Night
outside of the broader context of the album. The entirety of that album was made to be raw outpouring of anger and grief, a catharsis for Young's emotions regarding the drug-related deaths of guitarist Danny Whitten and roadie Bruce Berry. The fact that the songs were recorded intentionally rough and "real" is now the stuff of legend.
What's not as well known, possibly because it slightly tarnishes the cherished mythology, is that the run sequence of the songs wasn't nearly as improvisational as the songs themselves. The song order was shifted around many times, in fact. This is of interest to "World On A String" because of the premeditated role the song plays in the full album experience. It is an up-tempo shift, which is kind of amusing because the song's a far cry from being a dance number.
It's still a brooding sort of song, but within the borderline-suicidal context of Tonight's The Night
, it's roughly akin to Bobby McFerrin's "Don't Worry Be Happy