It's not easy to put on a monkey suit and put up with forty hours a week of bitching customers, temper tantrums from your boss, and sales quotas. It's also not easy to make a living in music. A day job is much more than free Post-It notes though, my friends. You might also find out that the dream of being a working musician is much more fun than the reality. The music business is anything but what MTV wants us to believe.
Many people find it worthwhile though.
I know I do. A day job is a double edged sword. I almost never advise a band to quit their day jobs right away. It's not going to be easy though. Bands who want to make it in the music business need to treat their music career like a second job and working two jobs is never easy.