This feature would only be interesting for bigger holders.
Voting with full power drains 5% of your voting power, to recover it you need to stop for a while. Rule of thumb is 20 votes with full power a day.

I'm not one of the biggest whales here, but my vote with full power already gives 7$ or so. I'd like to adjust that value, enabling me to spread my votes and the resulting rewards over more posts. Right now I don't vote for external links, videos or pictures at all, because I prefer posts that took the author some efforts. When I could adjust the voting power I'd give funny posts or interesting links a small upvote at least.
And I do know for certain that this is even more true for at least some of the bigger guys.