Points of Interests & Incidents

[OldMariner]

So i found several of tjos "incidents" sites, marked with a skull on the map, and the yellow icons marking points of interests.
In some of the points of interests ove found treasures, others there were nothing interesting abput them.
Whats the purpose of the points of interests really ? And the same for the incidents sites with the skull icon, what are they for ?
Thanks for helping me understand :D

[OldMariner]

Up

[Connobar]

Sometimes I'll find a chest near accidents, but some are just a cart.