Your voting power only depletes at a 2% rate of what's left every time. Which means it's impossible to actually get to 0, although you could get to 0.0001% after maybe millions of votes. It takes 5 days to regenerate from 0 to 100, or 12 hours to regenerate 10%.
Keeping your power up is only important if you're seeking curation rewards. The only affect is how much rewards you can put out at a time, but it takes a lot longer to deplete your power if you scale it down with the slider. That's the purpose of this experiment. Finding the sweet spot that allows my power to regenerate even while I vote casually like I did when the optimal limit was 40.
No, part of the importance of your vote is the direct benefit YOU ARE GIVING to the person you vote for, and to a small degree the entire community.