One good thing is that it keeps Wikipedia a tertiary source. I personally have a fairly inclusionist perspective, but my perspective is more or less: Wikipedia should cover anything on which any decent third-party source can be found (and it should point the reader to the source, so they can look it up themselves if they want).
There is of course stuff on which internet users can collect useful information, where no current sources exist to cite, but there's no reason Wikipedia has to be the only wiki on the internet. For example, Know Your Meme is an excellent project to document current internet memes, including via original sleuthing by its editors, who try to track down the history of memes and reconstruct their paths. It's not really a tertiary source summarizing the existing literature though; it's a sociological/historical research project. And it's great that it exists. Why does it have to exist on wikipedia.org, a project that has different goals, which don't include doing original research? Of course, memes should also be covered on Wikipedia, but only when Wikipedia can cite some existing published source documenting the information (a news article, a sociology conference paper, anything really).
I guess it seems perfectly fine to me that there's more than one project on the internet dedicated to collecting knowledge, with different goals; I don't see why Wikipedia has to be the union of all possible wikis. If anything, I would prefer more projects with different goals and approaches to exist, rather than everything being so centralized. That way I can go to Wikipedia if I want the tertiary-source take on internet memes, and I can go to Know Your Meme if I want the primary-source take on internet memes. Same with a Wikipedia article on a location versus a Wikitravel article on a location: both useful, but I don't see why they have to be merged into one project (or why that would be helpful).