A hit single, or preferably a string of them, opened the way to all the other little earners that generated a substantial income, determining the band's position on the bill on a package tour, maximising exposure on music-based TV shows, getting the act a slot on a TV variety show…
And the hit single, in the standard business model generated income and royalties for the artist, the record company and associated hangers-on based on the number of times you could get the punters to buy the actual song.
First, of course, there was the single. The record company then could, and often did, take the song, add another three (preferably including another single) and repackage them as a four track EP (Extended Play). That didn't always happen, particularly in cases where there wasn't much recorded material to work with, but once you had more than a dozen tracks there was the possibility of an album (or LP Long Player), and if there was a relatively lengthy career you could squeeze in a Greatest Hits or Best of package as well. So with that Decca From The Beginning Small Faces album you can see the record label and the former management operating in milk it for all it's worth mode.
At the same time there was a new, hipper, business model emerging, based on the avoidance of repetition, and you can see it kicking in with the Immediate album. In this setting you didn't put the hit single on the album, dismissing that practice as an exercise in ripping off the fans.
This model tended to be favoured by groups that wrote their own material, since it meant that they were generating maximum royalties as they had a go at the premium end of the market.
You can see this kind of thing emerging with the likes of the Rolling Stones Between the Buttons, Where the preceding album, Aftermath, included Mother's Little Helper, Lady Jane, Under My Thumb and Out of Time, the twelve tracks on the British Between the Buttons didn't even contain the B-side of a single.