Positive Cabin Pressure Differential on ground.
I can't comment on modern two-pilot RPT aircraft, however in the days when we old coffee drinking, sandwich eating Flight Engineers were carried I know we did not pressurise the airframe during ground operations. Depending on which aircraft being flown, e.g. C130 Hercules to B747 and others in between in my case, the pressurisation was not introduced until airborne. This may have been via manual selection or automatically once airborne. There was no structural reason ever mentioned, primarily the operation of doors was the consideration. Plug type doors would be difficult to open with positive differential pressure applied. Flight engineers, at least those I know and worked with took pride in making the cabin environment as comfortable as possible by handling the temperature and pressurisation systems with thought and care. In some cases where performance requirements demanded it we would do "No Bleed Offtake" take-offs to get maximum engine performance, which I would suggest rules out any structural considerations in relation to the pressurisation system during ground operations.