I can't think of times where I've liked it as far as inventory and abilities go.

My all-time favorite example for a "taste of power" is Pankratz/Papas from Dragon Quest V. I don't believe you ever really control him directly, but the way he decimates enemies before your character has any opportunity to act perfectly shows how much more powerful he is and how weak and fragile you still are (kinda like Sephiroth in the Nibelheim flashback, but in this case it's used to admire your avatar's father). It makes the dungeons you explore without him feel especially dangerous, but in the final dungeon of the child arc, you're fighting side by side with him and actually pulling your weight for the first time. It really gives a sense of finality to that chapter of the game.