also rotation rate is affected by the actual aircraft perf. really heavy rotate slower, really light, faster, mid weight mid perf rotate @datum rate. don't want to do all that then rotate at the rate scheduled in the afm. i.e datum rate
I am not sure you are right Rhovsquared. Apart from the engine failure rotation the Boeing 737 FCTM advice on rotation rates does not differentiate between light weights and max gross. From observation I believe that with a light weight and thus a rapidly accelerating aircraft there is sometimes a tendency to hurry the rotation where the pilot perceives the airspeed is rapidly building up just after lift off before he is ready for it.