When you obtain STEEM, you can power that up to STEEM POWER to increase your vote value. Getting STEEM POWER back to STEEM takes 13 weeks, but you can lend out your STEEM POWER safely (total control remains for you). Lending STEEM POWER out serves the purpose of temporarily making other users vote more valuable, until you decide to take the STEEM POWER back
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From @gomovies