Game Development

Honestly, I thought the character touching plain walls was a great way to support walking across or sliding against walls, which is common in games but doesn't make physical sense. When the character puts out their hand it can indicate that the character keeps its distance from the wall.

You may not put out your hand when walking along walls, but when you're pushed into them, you may very well put out your hand.

Another way to interpret it is the character indicating the restriction of the player's control. While the character will follow the directional input generally, when there is a wall, they want to and have to evade that. Putting out the hand gives it a human touch of looking for safety too - which could even lead to players keeping a little bit of distance to a wall when walking alongside it.