Head tracking can be useful when your dogfighting. You can turn your head and track that extra bit in the canopy to your 3 and 6 o'clock, the other use it to slave gimbaled weapons to head tracking so they follow your eyes essentially
But.. but.. if you turn your head and the view rotates correspondingly, you have to keep your eyes focused center screen to get the benefit. Please let me know if I'm thinking about this wrong. For example you turn your head to the left, but have to now cut your eyes back to the right so they are focused center screen, where the view has now rotated to the left. This seems completely unnecessary. Now, if you have a screen attached to your head (like a VR headset or w/e) then this makes perfect sense.
edit: the slaved weapons that track eye movement I can see being useful.