Palm muting is quite a versitile little trick really. There are multiple degrees of palm muting, like a slight mute which has your hand barely touching the strings, the standard, which slows the ringing but gets a good and gritty sound, then the full mute which is basically just stopping the notes from really sounding. I find that I can get some quicker riffing when I use palm muting and it helps to build tension and aggression. At least it does with some of the stuff I write. Of course you can mute individual strings with or without distortion for a whole new sound and style. Palm muting while finger picking as well can offer a whole different feel.