Please explain how.
By haveing 1/3 to 1/4 the crew there are limited open spaces needed. Thus a smaller, more effecient ship.
Fire suppression and closing off of damaged areas to smother a fire, even flooding and area, is much easier with few crew.
Remote sensors and tele-operations can be directed form a central damage control area.
Not just damage control but almost all areas of the ship would be automated. The DD-21 was supposed to be a updated destoryed, unique in that 3/4 of the crew were not needed.
The DD(X) is what happens when a good idea goes before a committee!!