Your face and head will be supported. So you won't be slumping. And getting pain in your neck when you wake up and you're gonna look like a genius.
How big of a pillow can I bring on a plane?
This differs from airline to airline, but as a standard rule, pillows are allowed on a plane as a personal item if they are reasonably sized. This means the pillow can be stashed under the seat or in front of you.
Is a square or round travel pillow better?
Round cushions can be a game-changer if you've found that squarish designs aren't for you. They allow your head to sink into a central position and provide support on all sides.