So, as an example, could you decide to ride on a banned road knowing that you will get a 1hr penalty but that it will save you 2hrs of riding ?
In practice I don't think people do that, in part because they don't know what the penalties are so don't have the info to make the 'professional foul' calculation. However, I also believe that if people reckoned that they would get a really big penalty (or get disqualified) they might behave differently sometimes.
The philosophy behind the penalties is that they are designed to compensate for unfair advantage, not to punish. The basis is that they accept that anyone can make a mistake but it shouldn't affect the result. Like my bridge ^ it was a genuine mistake, I didn't see any indication on any map that it was not rideable or any signs on the road. So I would expect to have the time advantage I gained from it vs the next best route wiped out by a penalty. If someone was to make a deliberate mistake, ie cheat, they would expect to be disqualified rather than receiving a time penalty.
In the past I've said that I think the penalties are not enough to outweigh the benefits of taking the illegal road. This was based on my experience in 2016 when I leapfrogged with another rider for much of the race, was slightly ahead of him when we both slept at Skopje, but he finished about 12 hours before me, with a 2 hour penalty.
How did that happen? From Skopje, I took a rough and hilly but legal road while he took the motorway (waved onto it by a policeman). Not only was his road far quicker but it meant that he was able to finish on the Friday evening, while I had to have an extra sleep stop which took me into Saturday morning.
If we had taken the same route I may not have beaten him but I think we would have finished within a couple of hours of each other.