IMHO, Wikipedia is mile wide and half a mile deep.
Apart from knowledge special to a particular thing, it contains pretty much everything. If you ever think it is not the case, it is certainly the place to put your additions to instead of your private bookmark.
I'll grant that Wikipedia has certainly gotten better. (And continues to do so!)
But it still tends to have large blind spots where the source is (a) pre-digital or (b) of interest to a relatively small total number of people.
Try heading to your local library or a used book store (Goodwill works in the US), find a technical or history book older than ~1980, then attempt to find the content in Wikipedia. Especially in history, the hit rate isn't good.
> the place to put your additions to instead of your private bookmark
My private bookmarks won't get deleted by a zealous reviewer five minutes later.
It can be hard to contribute to Wikipedia without enmeshing yourself in the politics of it to protect your contributions from deletionists. This gets covered every few months on HN.
