Well, for one thing, the LP (the 12" vinyl disc, played at 33 1/3 rpm) made the album a more or less standard unit of a musician's output.

Prior to the LP, in the days of 78 rpm discs, albums were literally albums, big notebooks with paper sleeves. You'd collect your favorite songs and B-sides by Billy Murray or Eddie Cantor or whoever, and compile them into your album. Singers produced singles.

We seem to be going back that way now, with mp3s replacing CDs as the dominant medium.