Fleeing is something you should use, if you accidently triggered a fight, that you most likely won't survive, because the enemies are stronger as you expected.
If you return you still will have the knowledge and be better prepared, but same goes if you start a new playthrough. But killing a 1, 2 enemies and afterwards fleeing before you self get killed, is no cheat but exploiting the game like save scumming or using sneak in the open.
It denies yourself a real challenge, making the game two easy. It is impossible to balance the game against these exploits.
