Why Does a Standard Retention Knob Deform a Toolholder?

When a standard retention knob is installed into a toolholder, the threads create torsional stress that deforms the thin walls of the toolholder.  A retention knob is like a fastener or screw in that it relies on four threads of the fastener to be installed to reach 'full engagement.'  The first engaged thread from the flange carries the most stress; the balance of stress is unevenly distributed through the threads with the last thread having the least amount.  This uneven stress distribution is placed on the narrowest cross-section of the toolholder and deforms the small end of the toolholder.  This taper deformation prevents the toolholder from having full taper contact with the spindle.  What difference does it make if my toolholder is deformed?