The wall is plasterboard with a thin coat of plaster to make it look nice. Or a brick wall with a thicker coat of plaster to make it look nice.

If you didn't have the skirting then the joint between plaster and floor would have to be absolutely incredible to look nice. Probably double the time it takes to do the job.

Easier to cover the shabby looking work with a plank of wood. Same with coving.