While using vehicles within ARMA 3, such as fast moving jets or planes, the system has a MaxFOV set for when the vehicle is in motion and reaches max velocity.
This can create a cool "movement" effect, giving a sense of speed, however it can also cause disorientation and motion sickness for players who are used to simulators that do not make use of such features. In fact, this feature would closely resemble features of arcade games such as NFS: Shift, whereas most simulators tend to lock the FOV in place.
This can be counteracted by using the ZOOM functionality, however this tends to leave the view too close, depending on the monitor setup already.
Futhermore, situations where players are passengers, such as inside the back of a plane or helicopter, causes a fisheye lens even though there is no movement in front of the player.
Making this feature optional would at least prevent people like myself from getting motion sickness due to this sudden change in FOV that is not controlled by the player. (in particular players like me that use a 45 degree horizontal FOV in other games like racing sims)
For this reason I often opt not to ride in vehicles, even though I'm perfectly fine in any other game.