An interesting look at rotation from Adrian Clarke, looking at both the numbers and citing his own professional experience:
From memory, playing four matches in a short space of time can have a negative impact on sharpness. I remember lactic acid building up, muscles getting weary and at times running on empty, physically and mentally, by the time the New Year’s Day match came around.
Everyone handles strain differently though, and age is also another factor to consider. In my teens and early 20s I did not feel at all tired two days after a match, but later on in my career those recovery periods became noticeably longer. It is a manager’s job to know how heavy a workload each of his players can tolerate.