The MA3 and MA4 carburettors which are common to most of these engines, and are installed (MA3) on the O-200 in the 150, contain additional jets for idle and very low power, principally to aid engine acelleration. Once any significant power is selected, the engine is being supplied fuel by the carburettor main jet, whose mixture is also pilot controlled. Presmuming that the pilot has the mixture control full rich (and the carburettor is set up correctly in the first place) the use of partial power cannot cause harm to the engine. If it were to cause harm to the engine fvor takeoff, flying at anything less than full power in cruise flight would also be causing that harm. Operating the engine for a partial power takeoff would be the same as operating the engine for cruise flight, just you began stopped on the ground. (This presupposes that a maximum performance takeoff is not required for safety).
All that being said, I'm not advocating partial power takeoffs for any reason other that pilots practicing technique and becoming more aware of aircraft handling. In certain operations, partial power takeoffs benefit aviation as a whole, in creating good public relations. (noise abatement)Most takeoffs, however, would be presumed to require full power to be conducted safely. Engines benefit from being operated at full power too.
Pilots from time to time experience unusual events. Safely practicing operating an aircraft outside the "norm" though still within it's limitations is an excellent way for pilots to be just a little more ready to handle an unusual event. There certainly cases where an otherwise flyable aircraft, albeit with a defect, has been crashed by a pilot, who perhaps a little more prepared for the unusual event, would have completed a safe flight.
Safe and appropriate practice is always a good idea....
Pilot DAR