First, you might want to listen to the Beach Boys song Sloop John B, just to refresh your memory. Then a look and listen to the video Behind The Sounds: Sloop John B will give you some nice insight into the recording and arranging process and open a window onto the keen production expertise of a young Brian Wilson, directing a roomful of seasoned session pros (none other than the Wrecking Crew). It's how they used to make records, kids!
Bands often don't seem to be able to play on stage the way they did on their album; and we accept that for a lot of reasons having to do with the conditions, the production facilities and the sheer number of takes that were probably involved. But for a whole generation of hit music, there was often a more basic reason: it wasn't them playing on the album in the first place.
For nearly a decade, if you were an L.A. producer and you wanted to record a hit single, you'd call in The Wrecking Crew. Members of The Byrds, The Beach Boys, and The Mamas and the Papas would step aside as The Wrecking Crew laid down the instrumental tracks. Then, the members of the main band would come back to add the vocals on top.The above link goes to the OPB radio story I listened to this morning, with an embedded player. Official site for the book.
Today in 1966, Brian Wilson starting laying down instrumental tracks for "#1 Untitled." Eight months, 90 hours of tape, and $50,000 later, he released his "pocket symphony." [more inside]