Well its not absolutely necessary to be online 24/7. You will still get your rewards if you remain online for few hours but it will take longer to get your reward. Also you have to do something more than just sitting on your coins to get reward. I mean why even come online for a little time every 20 days, just get your rewards for creating a wallet. Current POS system is dumb, thats why i called it rent seeking as people aren't helping the network but keeping coins just to get free rewards.