The final game of my favorite series of all time, Quest for Glory 5, you get a shrink spell. It does exactly what you think: It shrinks your enemies down to 50% their original size... and then when you cast it again, they flee when they get too small to do anything to you... and you can still cast it on them as they flee and shrink them down further and further.
I... just never used the spell. I mean I did want to maximize all of the skill level of my spells (but there is no discernable effect to the skill of that particular spell). It just felt really needlessly cruel. I imagined the enemies going on a Honey I Shrunk the Kids type adventure, only it is much shorter and extremely brutal...