A refueling Space Station is a structure outside the orbit of HOM created for the purpose of refueling other space vehicles while they are on a journey.Such a Station is built up of a lot of "Station refuel Silos"
Station Refuel Silo : http://spaceagency.wikia.com/wiki/Station_Refuel_Silo
-Can be used as a refueling stop for vehicles doing long journeys
-Practically a limitless supply of fuel
-Lower power consumption
-Lower number of Resupply missions
The ideal proportion for a Refuel Silos to other modules in a structure made for exploration is one Refuel Silo for 3 other modules.More Silos will create extra fuel consumption made to carry the extra fuel and less Silos will reduce fuel storage capacity of the structure.
However,A Refueling Station has relatively a large number of Silos to other modules making them terribly inefficient for travel.Also,even if the fuel in one Silo is over,the Player can't eject it until the fuel from the Silo opposite to it at the flip side of the line of symmetry is over and ready to be ejected.
This is because ejecting only one silo from one side will put the center of mass of the total structure off from the center of thrust causing it to spin with acceleration.
Due to this,A Refueling station is generally not used for space travel.
Also,due to the large mass,it is quite difficult to spin it,and to accelerate it,as the inertia is higher.