In addition to that, I figure Yeoman Rand was also Kirk's "batman," meaning all around personal servant. The less time a captain spends taking care of personal matters like housekeeping of his quarter, cleaning his uniforms and fetching meals/coffee, the more time he has to deal with ship's business and command descisions.
Yup. I figured that in "The Corbomite Maneuver," Kirk was used to having a male yeoman as his "Alfred" (to use a Batman reference), so he was uncomfortable suddenly having a pretty female yeoman suddenly taking that role and being aware of every single detail of his life both on and off duty.
KIRK: When I find the Headquarters genius that assigned me a female yeoman...