Record companies in the late 50's/60's preferred Mono because the groove on the vinyl was smaller and they could fit more music on an album/EP. Needles on most Hi Fi's had two sides, one for Mono, one for Stereo, so, it wasn't perfected for awhile, and just when it was perfect, out came CDs. Round and round we go, pardon the pun. Since the Beatles have been my religion for so long, I don't know if there are significant differences on Stones/Who/Kinks/etc. albums whether they are mono or stereo. And I don't really care.