Watch the Palm Muting online guitar lesson by Jeff Scheetz from Rock Tricks
The key to our palm muting technique is finding the right place to have your right hand touching the strings. Too much and you kill the strings or change the pitch, too little and you get too much ringing out. So, once you find the right place you can get some great effects.
Heavy tunes usually have some muting simply for dynamics sake. Sometimes you can change the feel of the song completely without actually changing the chord structure just by the way you palm mute.