This value is the amount that the tool edge clears the chained geometry. All face methods use this value at the beginning of the first cut per pass.
Zig Facing Method
Side Clearance is used at the beginning of all cuts.
Side Clearance is used at the end of all cuts when the Clear Part on Every Cut box is checked.
Side Clearance is used at the end of the last cut per pass when the Clear Part on Last Cut Only box is checked.
Zig Zag or Spiral Facing Method
Side Clearance is used at the beginning and end of all cuts when the Clear Part on Every Cut box is checked.
Side Clearance is used at the end of the last cut per pass when the Clear Part on Last Cut Only box is checked