It depends on your perception if bounties are a waste of time  or a great passive income. In my opinion it is not a waste of time nor a passive income. Bounties can give you coins if you have no money to start an investment, you'll just have to do some task first in order to earn coins. Because of the many tasks that you can do in regarding bounties you can say it's not really that passive because it can take your time doing many things.