It is equal to add static route to null interface if u r familiar with Cisco concept
Simply it is adding static route in your routing table without next-hop and if the router receive PKT for this destination, it silently drop the PKT.
It is used mostly for route advertising, so it you have 4 subnets 192.168.1.0/24, 192.168.2.0/24, 192.168.3.0/24 & 192.168.4.0/24 and you want to advertise summery route 192.168.0.0/22 only so u can't without have valid route in your routing table. So u can use this feature to be able to export that route