Without this mod, rotating the camera around to see better from inside a train can be very annoying, as the game feels like it is fighting you quite often. With it installed, you get to rotate the view while driving or a passenger.
Even better, the mod sets the position of the camera properly. Now rotating your view around won't orbit your camera in a big arc around a central point, instead you get what you would intuitively expect: the view rotates while you stay fixed in your seating position.
Further, this mod properly enables wagons have front and rear driver's seats, something that didn't make sense when you had to stick the player's view close to the centre of the wagon to let them look well enough out both sides and still be able to escape by right-clicking the wagon's hitbox.
Of course one day maybe we can hope that we won't need this mod, because it only exists due to a deficiency in the game engine. But it's very good to use right now.