The detrimental effect on engine power due to increasing cylinder head temperatures caused by unnecessarily extended engine run up's, should be taken into account.
For example, the Convair 440 Metropolitan (Pratt & Whitney R2800 engines) had BMEP gauges which in effect measured engine horse power.
During the take off run and initial full power climb, the BMEP would show a gradual decrease as the CHT's increased. If the CHT was already high due perhaps to extended running at high power to clear fouled spark plugs, the drop of BMEP from standard take off reading , was quite noticeable. Typically one would expect 235 BMEP (left engine) as the throttles reached the take off limit manifold pressure at standard OAT, but by the time the aircraft had reached 200 feet the BMEP had dropped to 225 or thereabouts. Obviously this gradual decay in power could make single engine rate of climb reduce from optimum for the conditions.
From that it was clear that run-up's for engine testing on the ground should be as brief as practicable in order to obtain the best BMEP for the conditions. Ths same principle I presume would apply to CHT increases on light twins such as the Chieftain, Baron etc. The habit of "burning out the plugs" at high power if the mag drop check is outside limits, is a two edged sword. High power on the ground causes increased CHT's. The spark plugs get cleared eventually, at the cost of reduced engine power on take off.