well, with regards to GLA/EDI, GLA has the transatlantic links (CO to EWR all year round, AA/AC to ORD and YYZ respectively during the summer timetable), while EDI has the direct flights to Europe (LH to FRA, AF to CDG, etc, while almost all of GLA’s European flights have en route stops at either BHX or MAN).

It just dosen’t seem to make sense with regards to transfer pax.