I am fairly certain that power is not something that is equally distributed among human beings. I am also fairly certain that individual power is going to fluctuate depending on circumstances and relationships between people.
In the context of voting, I am attempting to influence the direction of a much larger source of power. If no one attempted to do this, that larger source of power would still exist. It almost seems pointless to try and exert any influence since the power of an individual anonymous vote is infinitesimal compared to just the power of me deciding where I might shop for groceries. Bordering on almost non existent when considering how that vote might influence the massive social structures in a country of 300 million where that country is also dealing with external influence of a world of 10 billion.
Yet, that act, no matter how small and insignificant as it may seem doesn't give or take any power from anyone. It only expresses an individual will. It's a token reminder that as an individual, I have power that may influence another. Regardless if it does or does not it's still an expression that cannot simply be ignored. I am going to vote one way or another. So will you.