If the steel is boxed in and visible in the room 'underneath' the ceiling it's going to be much cheaper than inserting the steel in the floorspace so the ceilings from the two previously separate rooms become one ceiling once the plastering is done .
Similar consideration to supporting the ends of the steel . If the steel is inserted in the walls taking the load with padstones /small steels 'hidden' in the brickwork ( if that's even structurally possible ) It's a lot more money than the steel support (e.g. 9" brick peirs ) being in the room .
I mention this because very nice houses often have two rooms knocked through on the cheap without much consideration and the resulting boxed in steel and support looks cack.