I find it helps to always be aware of the route the GPS is trying to take and why. Sometimes I even go a different way from what is suggested. That's probably the older gen in me speaking but it not only assists with general awareness (probably that hippocampus lighting up), but sometimes gets me out of potential navigational stuff-ups.
Doesn't have the stated affect on me, I'm always trying to figure out the lay of the land as I'm going along and if I would not take a different route. I don't have to reuse if I've driven a route with it once.
But it is useful for rerouting interactively due to updating itself due to traffic build ups.