Pippin Williamson wrote an open letter on side projects that's well worth the read.
Side projects inspire us. They give us much needed reprieve from the daily grind of our day-to-day work life. They breath new life into what we do and who we are. Side projects are often where we find true passion. They are where ingenuity and brilliance truly shines. They are responsible for some of the greatest products that we all know and love (or maybe hate) today.
But there are bad parts too. It's just a balance.