The amount of steem is doubled every year, 10% is whats being used for payouts, curation rewards, and for new users to sign up. The other 90% is paid back to steem power holders, so in reality the inflation is 10%, it just depends if you hold steem power or not. Thats the incentive to hold Steem Power instead of Steem and only use Steem when you want something with higher liquidity to sell out or buy in. Steem Dollars offer a higheer liquidity as well but they only pay 10% interest yearly.