The cut height I use depends upon: (1) Time of season, (2) Quality of turf. It has been over 10 years since a customer asked me to cut at a different height. I make the decisions on what time of the season, and what I have to work with on their property. Nobody complains, or says anything (positive, or negative). They rely upon my judgements, and probably never realize that I am changing heights.
I usually start the season at 2.5", regardless of lawn. Some of the poorer quality lawns go up to 2.75, and never go higher. Others start at 2.5 (April 1), then 2.75, then 3.0, ... all the way to 4.0 by June 1. Many reach 3.5, 3.75. After September, some heights will change downward. The last cut of the season is intended to be back at the 2.5 that was used at the start.
I also make decisions regarding area. Small areas in front or side of the house my be cut 1/4" or 1/2" lower than an open backyard.
My rules are very flexible, and attempt to do what is right for the time and situation. My customer journal has records of what was done on each visit.
I use a Honda hand mower, and Exmark 36" Viking (fixed deck - yes, I only make changes on the caster spacers, not blade spacers), and a JD ZTR, 48".