Corridor seats on the TGV — why? Are seat reservations not always mandatory?

The TGV has mandatory seat reservations (unlike, for example, the ICE). There is no equivalent of German Flexpreis where I can take any train, and if I miss my connection I need to get a new ticket issued. Yet on the TGV, there are often small foldable corridor seats, which do not have seat numbers assigned. When travelling on TGV, I've often seen those in use. What is the purpose of those seats? My impression is that in case of disturbances, the mandatory seat reservation is not well enforced, but I don't know if that is at the discretion of the train manager or if there is an established policy.