[Dadams1]

Well, Shadowkeeper is also useful if you make a stupid (D'OH!) mistake like having one of your party members die then forgetting to pick up their stuff AAAAAAAH then when you come back it's gone! With Shadowkeeper, you can just re-give them the stuff, and it's not really cheating since losing it was an accident. As long as it's the same stuff.
Anyway, if you really wanted to, you could beef up your main and powerhouse through the game with all the good stuff, armor, weapons, etc... I've done it before, it's pretty fun.
It's also good if you forget to get an item because it's your first time, such as... [Possible Spoiler]
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The Sword of Chaos +2 in Irenicus' dungeon. I missed it the first time, and got really angry at the game hehe, but the next time I got it yay.
Anyway, Shadowkeeper is also useful for, as Nerull said, changing things you don't like about your NPCs without abusing it. That's all I can think of for the moment. Oh, and it's also decent for over-xp glitches, etc...