As a musician you sometimes need to imagine yourself in the position of a music listener. Picture this: you're at a concert approaching the merch table. You see a vinyl release of the headliner's latest album, and while you may want to snatch it up that instant, who wants to hold a record for the whole night? You don't want to obsess over it while trying to balance your beer, or protect it from elbows and mosh pits. So you say you'll pick it up at the end of the night, and next thing you know the show is over, you spent all your money on drinks, or you simply forgot to grab a copy on the way out.
Now picture a similar scenario, but instead of seeing only a vinyl release, you also spot the CD copy of the album. It's small, you can fit it in your jacket pocket or bag/purse, and suddenly you're free of stress and have freedom of movement. You buy it on the spot.
CDs move at the merch table. They're easy to pack in boxes, lightweight to lug up the stairs of venues, and don't take up much room in your van on tour. You're not only selling your music, but peace of mind.