I have a 160 degree thermostat, and I have my chip set to turn the fans on "low" at 176 and off again at 171. Even on a 50 degree day, while I'm driving, my coolant temp will cycle between 176 and 171 as the fans turn on-and-off. Read: There is not enough air flow going through my radiator to keep the coolant temperature down, so the fans must run to do the job, even when I'm just cruising down the highway at 60 mph. Since my "Ramcharger" fans are wired the same way everyone else does, they go to "high" speed when the ECU energizes the low-speed solenoid. This means the wear-and-tear on the fans and electrical system is full-blast whenever the fans are running.
I'm pretty convinced that on that same 50-degree day, the fans could come on "low" and still keep the coolant temp below my 176 set-point. .