One Leg FlightsFlights One Leg
They are useful dates when trying to find the cause of an incidental error in a particular avionic. Error records usually record at least 20 sections before they "tip over" and override old datas. On some planes that fly 6 or more stages per flight per night, this will ensure that the airplane can reach a service basis before the error is overridden.
I saw mistakes that only occurred on the first leg of the stage after the airplane was left at a very wet aerodrome over night. Restoring the condition enabled us to reproduce the error. But I don't think the route is important for both planes, no carrier. Most flights have one or two stages for economical purposes only.
Aeroplanes must be run at relatively high capacity in order to be viable. When you have a line with fewer people, you really want to use a smaller airplane or use it less often. Since different connections have different requirements, it is rather uncommon for there to be many successive connections with similar demands, so that it would make good business of flying them on one aeroplane as a multihaul one.
Only a few would want to travel the whole way, as the stopovers take quite a long time. Aeroplanes are not about leg, but about cycling, i.e. pressure application cycling. In pressurised aeroplanes, stress relaxation is most intimately linked to cycling, and since each cycling includes a periods of high thrusts, there is also some associated deterioration of the power plant.
Irrespective of whether the airplane collects 4 circles on a 4-stage voyage or 4 separated voyages, what is a mileage? An air route is a voyage of an airplane from take-off to arrival. The use of the word implicates a multi-part ride. Passengers consider it to be part of a voyage that may begin or end with a stop, a transfer of planes or a transfer of airlines.
Refer to Jan's response regarding airplane cycle times. Have a look at other issues that have a tag that drives the trip datalogger or ask your own one.