From Kirk himself...
"If you look at the side of your hand, right below your pinkie, you'll see there are some wrinkle lines. At least there are on my hand... [laughs] Because of my playing style, I'm constantly hitting the strings and palm muting and, generally, beating up my right hand. Over the course of a tour, those wrinkles start busting open and bleeding. I put tape over the wrinkles so they don't break open and bleed all over my guitar, 'cause if a string gets in there once your hand is cut --wow!--that stings! Plus, it lets me play faster since it reduces drag between my hand and the strings."