When I thought about demos, I used to imagine a shittier version of the final song: badly recorded, unedited, and with a sub-par performance. I used to label tracks “demo” when they weren’t up to snuff. It was never planned; f I was embarrassed to share something I made, I used “demo” as a qualifier, thereby excusing all mistakes.
Nowadays I have a better grasp of what a demo is. It’s a rough take of the finished song, not intended as a final product, but a necessary step in the creative process. All the essential elements are there, and the arrangement is done (to the best of your ability). When you listen to the demo, you’ll hear how all the parts work (or don’t work). You’ll discover what sections feel too long or too short, if the drums are meshing with your guitar, if there’s enough contrast from verse to chorus, if the bass guitar is boring, or any number of issues.
There are some things you simply won’t know until you hear them in context. These are changes you want to identify before final tracking. When making a demo, you’re not concerned with guitar tones, what the best mic is, getting great takes to edit, or editing at all. Your goal is to get the idea down, have it sound good enough, and learn from it. How will the final song sound? Once you have a better vision of what the song is about, going into the studio is fun because you know exactly what you’re going to do. It takes a load off your mind, and then you can spend more time experimenting with tone, knowing you won’t need to come back and re-record.
Even if the song is just guitar and vocals, I still recommend making a demo. You’ll be surprised at what you hear when it’s playing back. It’s counter intuitive, but while you’re playing you don’t notice everything, and the demo can reveal what to fix.
I’ve recorded songs with and without demoing first, and I highly recommend it. There’s always the occasion where my original demo was spot on and I don’t need to change anything, but that’s usually not the case. Most of my demos have been pretty bare bones, but I’ve found that the better the demo, the more you learn from it. That being said, don’t be a perfectionist. Make the demo, make it pretty good, and move on. Keep finishing.