Actually it is a way to quickly select a waypoint/markpoint/targetpoint.
By pressing the WP Increment HOTAS Buttton for more than 0.8 Secs you set the UFC to Quicksteer Action (QA). You then select which waypoint you want to use: Waypoint (Flighplan), Markpoint (saved position), Targetpoint (saved target position). You input a number on the UFC and click ENT.
The steerpoint will change to the selected one.
Waypoints: 1 to 60
Markpoints: 1 to 10
Targetpoints: 0 to 4
Targetpoints are not enabled yet, so there is only one: 0, which is your designated target.
If you input a non-existing waypoint/markpoint/targetpoint number, nothing happens.
It works like this:
You are flying towards Waypoint 3 but due to tactical considerations you need to go direct route to Waypoint 17. Instead of clicking WP Increment 14 times, or advancing the waypoint in the MPCD. You press the WP Increment long enough for the UFC to enter QA mode, select WYPT and then enter 14 and click ENT. The aircraft will now start flying towards Waypoint 14.