As you vote on Steemit, your vote power percentage goes down. As it goes down, it makes your full (100%) votes have less impact, giving less to authors and receiving less in curation rewards. Over time, your voting power regenerates, approximately 20% a day or a full refill after 5 days.
Right now, if we vote 10 times or less in 24 hours, the regeneration rate keeps up. So if you started at 100% vote power, cast 10 100% votes all at once, you'd go down to about 80% power. After 24 hours with no additional votes, you'd be back up to 100% vote power.