Free healing
Walking against a wall with monsters nearby allow for free regeneration of HP and PP.
Monsters doesn't get to act. Very abusable. IMO when issuing a walk command the game should check if it's not against a wall. If it is, just display "You cannot walk against a wall." or something along the lines and no time would pass. Alternatively, it could waste a turn (just like searching or doing nothing) a now monsters get to act.