Seat rails make each seat adjustable (to maximize on leg room) and to facilitate access to the cabin.

The seats are easy enough to relocate on the ground.  You add a couple of extra nut-sets during construction and when you are ready to move the seats it is a simple matter of backing out four machine screws, move the seat base, and re-install the screws.

But, if you feel like you would like to adjust the seats in flight then you will need this kit.  This kit is only for the front seats on the 750 Super Duty.