I think the worst consequence of this is that hostile armies in your territory get to conveniently retreat around on your land. Sometimes I attack a small stack to drive them off, and suddenly they're standing out of my reach, right next to a completely undefended castle town behind my lines. This really, really needs to change. As it is I basically have to match weaker stacks to get to fight them so they don't just run off to somewhere else in my territory. The whole situation is aggravated by the fact that retreating armies get to move in their turn immediately after you forced them to withdraw!