100 percent power up all your rewards goes to steempower. If you choose 50/50 half of the rewards are paid out in SBD and the rest goes to steem, which you can power up to give you more voting power. You don't lose it, and you can cash it out in 13 installments if needed. It just helps to have steem to build your account. For the first six months I powered up all my rewards. Now I cash out the steemdollars but the steem stays where it is...hope this helps. Ask if you struggle and welcome to steemit.