It depends. Depends on how far over distance one is prepared to go, how many other roads exist in the area that could be used to form the shortest route and how much the rider wants to go through particular places. Round here getting a 200 to be less than 210 with only a few controls isn't very easy, there are too many roads and some A roads that you just wouldn't ride on such as the A1. Autoroute selects it so one needs to put some other controls on the paralleling country lanes to a cause Autoroute to use them instead. If you don't, you end up with a route which is ~200km in Autoroute but when ridden is about 230km which in December is not desired. I wouldn't submit 12 or more for a 200 though.
I sometimes tried to run parallel with 'orrible roads, but several miles to the side. Autoroute is a funny creature. It still sent me on the 'orrible road, but when I tweaked the route it came out shorter.
It won't always work. Like you say, it depends on where you are. Quite often, the other option would mean lots of tricky navigation, which is OK if you have time to study the route or have a sat-nav. I struck a balance between an easy to navigate route, an enjoyable route, not miles over distance and cut down the 'orrible roads as much as possible. Most of my points chasing was done in Wales and Norfolk/Lincolnshire/Suffolk* for those reasons.
*Quite a lot of quiet A roads and B roads. The Norfolk Coast road was used quite a lot. A lot of people think it a busy road, but it's not bad if you're trying to get somewhere and rolling along at evens-ish.