Explanation
Each instance of VRRP running on a supported interface may monitor the link state of other interfaces. The monitored interfaces do not have to be running VRRP.
If a monitored interface loses its link state, then VRRP will decrement its priority over a VRID by the specified delta value and then will send out a new VRRP HELLO packet. If the new effective priority is less than the priority a backup platform has, then the backup platform will beging to send out its own HELLO packet.
Once the master sees this packet with a priority greater than its own, then it releases the VIP.

Explanation/Reference: https://sc1.checkpoint.com/documents/R77/CP_R77_Firewall_WebAdmin/92708.htm