Many moons ago BRAL used to run a CWL - CDG -CWL-BHD-ABZ - BHD - CWL - CDG - CWL as a days flying. You could buy tickets from ABZ to CDG if you wanted to and some people with a lot of time on their hands actually did ! What it did do was provide routes from three airports that were supported by pax from the others. Worked really well and made money where direct services may have been commercially marginal. Surprised Fly Be didn't extend to ABZ.