If you have a GPX file that has tons of waypoints - making it too big for your GPS or phone to handle, simply upload it to the FREE GOTOES Waypoint Filter tool along with your predicted route / course. Then specify the maximum distance from your course where a waypoint should be included. All the other non-pertinent waypoints will be filtered out so you have a smaller Waypoint file. This is useful on Garmin Devices which are often capped at 200 waypoints.
I typically use this feature when globbing waypoints from various bike packing sites. After I draw a route, I can then run all the waypoints against my route and filter it down to just the waypoints that matter for any given route/trip.