I made the mistake of painting a popcorn ceiling. I didn't want to remove it because I could see the formwork lines on a damaged part. I managed to fix that by scraping some off elsewhere, which I mixed with drywall mud and patched it.

It soaks up paint like a sponge. I was using a spray gun, but even then, I had to use a roller to force it into all the little craters.

It took 120L of paint to get decent coverage.

Would not recommend.