Re Star Wars Lego - Yeah - I meant in multi-player mode. I really don't see the point of it in 1 player mode.

Replay videos are OK - for example there are unlockables in some 2D shmups that show how to achieve big bonuses etc.

Having auto mode as a powerup that can be used a limited number of times would be good to get you over any rogue blip on a game's difficulty curve.

Some of the Mario Party games let you switch between human and CPU control mid game too (you can even select the AI level). There's lots of examples of this in multi-player - Chaos Engine was another good example of it.