I had not only that one but all the Warner Brothers "Loss Leader" sampler LPs ($2 each starting in 1968, by the late 70s they went to $3, stopping around 1980) I let a bunch of the later ones go, but still have the first 11, up to "Appetizers".
Sold by mail order, at first through ads in magazines like Rolling Stone then later with coupons on the inner sleeves of Warner and Reprise albums. Most were two LP sets, a few were single LP, including "Zapped" which showcased releases on Frank Zappa's Bizarre and Straight labels, and one a 3LP set in a box. The idea was to let people hear tracks from recently released albums that might not be getting any airplay. Some of the tracks would be rarities like single B-sides. The earliest albums came with booklets with a lot of info (text and photos) about the artists. I discovered a lot of music that way. Probably my all time favorite is this one which was the only 3-LP box set and the first one I heard when my brother brought it home from college. The cover is an homage to the old Warners Brothers cartoons.
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