I vaguely recall wrestling with this stuff early on in navexs and the first couple of hundred hours. These days I totally ignore it, it is just another set of questions that can be answered in an exam and has very little use in VFR flying.
How do you find out how many miles off track you are? Well typically by looking out the window! Do that and you know where you are (you must do how else do you know you are 5.8 miles east of track?). So if you know where you are and where you want to go, any of us can set course within 10 degrees - which is more than close enough. Simple VFR pilotage will then take you to your destination.
All these mathematical techniques really belong in the IFR area where you might get a decent VOR,DME or NBD cut which would give you a sudden 'you are x miles offtrack', for VFR flying putting an X on the map every 5 to 10 miles is so much more reliable that these techniques are nothing more than mind games.
If people are setting course and attempting to maintain it within a couple of degrees to arrive over some point within a couple of minutes of an arbitarily calculated time, then I would suggest they are not getting much out of their flying. They might as well use a flight sim and say a fortune! I fly to look out the window and visit places. If I ever fly a straight line it would be over the sea with no land in sight, otherwise enjoy our scenery and know where you are!
Of course you still have to know this stuff to pass the exams!!