In practice, there's not a specific distance but planning convenience. For short manually planned tracks (eg VFR planning), most people will plan from one visu

In practice, there's not a specific distance but planning convenience. For short manually planned tracks (eg VFR planning), most people will plan from one visually helpful waypoint to another, and measure the heading at the mid-point of each route segment. The midpoint approximates the GC heading, and anyway the discrepancy is (very) small on short segments. For long tracks (eg IFR interstate or intercontinental flights), most plans comply with standard routes, between nominal waypoints, and the route segments together may approximate GC tracks. Between each waypoint, one normally flies a constant heading. This is imperfect, but variations due wind and traffic are far bigger than losses due not quite conforming to a GC track.