Saw blades are still a bit of a performance issue for some people. We've worked on them to only cut in the direction they are travelling, and we've also reduced the "bounce" that used to be associated with them. When an enemy dies to saw blades, dozens upon dozens of voxels go flying every which way. A momentary framerate dip is the side-effect of that for some people, at least for now.
It is a beautiful display of destruction though. ;-)
-Cheers