The logic behind a pressure suit? Ask Dave Bowman
:) :)
In the Apollo example, if there was some sort of damage during docking, causing cabin depress., odds are it would be the LEM. (Simply because it's not as sturdy as the CM)
In that scenario, if the CM pilot is wearing a pressure suit, he can more quickly depressurize the CM, (Assuming the LEM is fully depressurized) and attempt some sort of rescue of the LEM crew. (Assuming they're also suited up)
I'm sure it was a real pain to don those suits, but in such an unforgiving environment, it does expand your options,...under some scenarios.