Of course not. All it does is charge your phone at the same rate as it does from a wall charger....the same thing that has been done since Windows Mobile days. People asked the same question back then too . If anything, it might cause a usb port to fail if it can't output enough power (would probably have to be an older computer).
It turns off one your CPU's cores when the screen is off to cut down on power consumption and improve battery life. The only thing is your phone can be slow to wake up if you're using a governor not optimized for it. Also, I've heard it can adversely affect battery life if you frequently turn your screen on and off, but I'm not sure how frequent is too frequent. I personally don't use it because my screen off battery drain is so minimal that I don't really think it's necessary.
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