I am very against the idea of using a Wiki to learn what I might be missing in a game. My best example of this is my first love, Megaman Legends.
In Megaman Legends you go around digging in ruins to find different parts, then you bring those parts back to Roll who sees if she can make anything out of the combination of parts you brought her.
Now I have played this game beginning to end at least 10x. And each and every time I play it, there is an excitement that in the back of my head, that I might discover a different weapon that I have been missing all these years. If I had ever used a Wiki, I would of never had that feeling because I would know exactly how many weapons there are and if I found them all.
This applies to new games as well, like Skyrim. If I look up a Wiki, I ruin the excitement of stumbling across something new or the feeling that I did it myself.