Do Not Plunge Straight appears only when you set Plunge Type to Ramp or Helical. For SRM operations, Do Not Plunge Straight determines whether or not to allow straight down plunge moves when the last tool reaches areas too small to perform a Ramp or Helical plunge.
If Do Not Plunge Straight is not checked, the tool plunges straight down in areas too small to perform the Ramp or Helical plunge.
If Do Not Plunge Straight is checked, the last SRM tool will not plunge straight down. Instead, those areas are left uncut and a message appears to inform you of those uncut areas.