It's an interesting topic. The question of whether you should burn a bridge or not is a matter of emotional investment in my eyes.
Usually, I don't burn bridges because in most cases, there is no point in doing that. There is either no harm in me keeping certain people or situations around or having them in the back of my mind for potencial future scenarios. Also, sometimes, burning a bridge may become a stress factor.
On the other hand, I see a lot of people who should burn certain bridges because the one waiting on the other side is just unhealthy for them.
Taking the Ex GF/BF example again here because it's probably the most notorious one.
You make some very good points. It can occasionally be a good idea to burn a bridge. However, I find it better to take apart the bridge in such a way that it can be reattached later if you so need it.
"Taking apart a bridge". Doesn't role as easily of the tongue as just burning it, but It's a nice way to describe it.