I use the feature you're discussing all the time, as a 'feint' move. If I face the enemy across 3 provinces, I 'feint' a small force to his strongest army, and bring my strongest army to his weakest point. I intend to retreat that feinting force (using the call off the attack option) - using it only to force him to keep some of his units to defend against my fake attack, instead of reinforcing against my main attack 2 provinces away.

It's only fair that the AI can use it too.