If you vote 100% and then I downvote because I think that is excessive, and then you reduce your vote to 50%, I've still used up my downvote mana. Similarly, you might make a big vote giving someting visibility and other smaller voters might follow on expecting the post to trend, generating curation rewards. Then when you remove/reduce your vote, the chance of trending is reduced and the later voters may regret their votes (despite potentially gaining relative curation reward share).

Good point!