Air Scotland do it to position the aircraft..they don’t carry passengers between the two airports!!!

I do believe you are incorrect. Have a look at the schedules, same flight numbers for EDI and GLA flights, same arrival times at their final destinations.
That’s winter, they probably do the same for summer flights too. I don’t suppose having just the one aircraft helps much.

http://www.air-scotland.com/otherinfo/flight_info.asp