There are a lot of situation where TrackIR can be usefull in a FPS :
- when you have deployed your MG, you can look quickly on the right and on the left to see your commrads or if any ennemy is trying to flank you
- when you're in a tank (it's easier for most people to know where you are looking for with a TrackIR than using a keyboard or a mouse)
- when you run in an open area, you can take a look on your flanks and don't loose time with your character especially if we are under a suppressing fire (we aren't crabs and it's hard to run quickly on the left or right like them)
- when you enter in a room, you can aim your weapon where the ennemy is supposed to be but you can look quickly if an ennemy is waiting you in a corner
...and a lot of other situations.
I've tried Insurgency Mod (HL2) with it and it's very usefull but for some reason, when TrackIR is activated, you can't lean (and the shorcut won't run too so it's a big disavantage).
And for people who don't know, there is a cheaper solution than TrackIR and it run very well, with the 6 degrees of freedom like it.
You only need a webcam with 30FPS and tinker a cap with the 3 necessary leds (really easy to make). Just take a look on
http://www.free-track.net/http://www.free-track.net/
In conclusion for me, a support for TrackIR or FreeTrack will be a nice feature but not as necessary than for simulators.