Reliable strong AP is mission critical to single or short hand. Driving for hrs on end... is usually boring unless in very spirited weather demanding you "steer" the waves. As OutB describes tacking... this is easy peasy... and unless you are constrained you're not short tacking... so it's little effort. I have to AP over steer the tack and then trim and steer as high as I feel works.
AP on a set course and when there are few corrections for yaw because of sea state should draw very little power. I can run instruments and AP on a sunny day if the AP is not doing a lot of "corrections" on a 110 watts of solar. Offshore I will run the diesel at least a few hrs a day to cool the refer (engine drive) and make hot water... and lift up the batteries.
The consensus is the AP is a must for a smooth and effective tack. At the same time for me the staysail should be self tacking without a club.