Most likely this is a company specific SOP thing. However, it could be something more technical, such as Special Instrument Procedures or Tailored procedures that are company specific.

Some procedures have "Terps Waivers" of criteria because of terrain, etc. Aspen for example has at least one procedure with 6 Terps waivers. Anytime you see unusual notes, such as "maximum speed 190 between xxxxx and yyyyy" that is a risk mitigating procedure to offset the Terps waiver of criteria. You might have another procedure which requires a precise track to be flown. The risk mitigating procedures (Developed by the FAA's AeroNav Procedure Team and reviewed by AFS-400 and the NextGen Branches) might include that the procedure note says "Use of Autopilot/LNAV Mode required"

Without getting too far in the weeds, this is all technical Part 77 Terps stuff described in the FAA's 8260.XX Series Orders.