One thing I can say for 100% certainty: You can not learn tactics if you autofight. If you chose to slug it out, you might win less, but you will learn new tactics in your wake.

You won't win every battle. Nobody does, or has historicialy either. The trick is to learn to do the best that you can do. The other night I had a _great_ fight that looked hopeless... it was my King and Prince and about 300 Vikings against 3500 Peasents. Talk about a slugfest I suprised myself by inflicted over 800 casulaties, capturing over 1000, and winning the battle, suffering less then 170 losses At the end of the day, the king had some nifty new virtues that I hadn't seen before. I doubt that the king would have gotten them had I auto-resolved... and I surely wouldn't have learned the merits of criss-crossing my flank advance