The Leatherman PST II was a ground-breaking model, introducing both scissors, and a part-serrated blade. Nearly all Leatherman models have a plain blade and/or fully-serrated blade.
A serrated blade is midway between a regular blade and a saw. It cuts through many soft materials more quickly than a regular blade, since you can saw back and forth and have the serrations "dig in" to the material.
NOTE: Sharpen the serrated portions of this blade carefully with a round or triangular file, and maintain the same angle (don't work on the back of the blade). A chainsaw file works well. Be sure to use extra caution with the serrated blade: it will cause much more serious injuries than a straight blade.