In case you vote before the post or comment is older than 30 minutes, you will win a share of the upvotes sent after your vote, called curation reward. The % of the upvotes depends of when you upvoted and increases from minute 0 to 30. In case the post is "power up 100%" you will receive Steem Power, in case it is a comment or the post have default payment, you will get Steem Power and Steem or Steem Dollar.

https://steemit.com/faq.html#What_determines_how_much_of_the_curation_reward_goes_to_the_author_versus_curators