Originally Posted by Iain Mac

In the Merc S Class (and probably others) the auto moving seats are there as a safety feature - if the car feels like a collision is imminent the front seats slide the occupants into line with the B-posts for maximum side protection while the front edge of the rear seats lift to stop passengers submarining under their seatbelts. At the same time, the sunroof will close and windows will either wind up or down so they are open just an inch or so to stop limbs flailing about outside the car and to allow the air displaced by the airbags to escape instead of hurting your eardrums.

Having the seats glide back and fore to make extry/exit easier is just a bonus.