Sit up straight like your mother taught you, and you might:
A) Be able to see something beyond the bonnet ("hood") and the A-pillars (i.e, the posts to each side of the windscreen ["windshield"]).
B) Have leverage to use your arms more decisively, thus be able to turn the wheel quicker and farther in an emergeny.
C) Be less likely to fall asleep behind the wheel.
But, hey, if lying down comfortably is more important to you than being a responsible driver, then by all means carry on.