Post rewards are paid in either Hive or HBD depending on the price of the two currency and the ratio of the value of the two currencies. When Hive price goes up the liquid rewards will be paid out in Hive. You can sell HBD for hive at the market from your wallet and power up to increase your stake to grow your account. Many people like to keep liquid Hive because it has greater liquidity and if the price suddenly hike they can sell high. HBD is pegged to 1USD and if you move it to savings you get 20% interest.

Hope this helps