Personally I wouldn't do this. I would re-create the route myself on RideWithGPS and use my version during the ride.
Reasons:
- I know that the version I actually use has been created using methods which are compatible with my Garmin and that it will work on the day without problems. If I'm using someone else's file, I don't know this.
- The process of re-creating the route, which only takes a few minutes, helps to acquaint me with the route. There are almost always details which I wish to change, such as a small diversion to a point of interest or a route through a town which I think uses a bad option. Sometimes there are minor errors, such as spurs, which get eliminated.
A big YES to this. I tend to grab other people's routes for these longer rides. I then use this as template to plot my own. Usually on the mapping software the route will be identified as NCN 123 and can easily be referenced.
Other people's might include diversion to a cafe, through a town for food etc. I like to plot the exact route, I can then deviate as I wish.
I also have a personal quirk to routing. I always put a way point before a turn and another a little after the turn. This helps ensure one gets the actual turn one wants. It's just a little quirk of mine.
I have friends who simply drop a waypoint 5-6 miles ahead. This can and does result in missed turns. There's one route we ride regularly where straight on is actually a right turn to stay on the same road! These little anomalies exist everywhere.