Following the interesting discussion… while still assuming (totally non-scientific)… instinctively… that routes (hiking, driving, flying…) which are not 100% identical are unlikely to have the exact (!) same length…
Now my two cents: as we are discussing flight routes we need to take into account that the earth is spinning while we fly. This means that even for the same (physical) distance say from Frankfurt to Miami it makes a big difference in flight time if we fly Frankfurt to Miami vs Miami to Frankfurt. The flight time from Frankfurt to Miami is usually much shorter as the earth rotates (west to east mainly) and thus while flying Miami gets closer and closer.
This difference in flight time also depends on which route we are taking (flying EDDF to KMIA usually over Greenland, then New Foundland and then coming down the US east coast… which by any means is not the direct route/line 
) and how far north the route goes.
So as it all comes down to how much fuel we need this is yet another aspect of planning a route.