This is a place to collect sources and assess the notability of subjects that do not (yet) have an article on Wikipedia, or whose article was deleted. If a subject isn't notable yet, a source assessment page is still appropriate: new sources may pop up in the future, but sources you find today may become harder to find due to link rot, so having a list of sources can be helpful in this case. It's also nice if editors don't have to dig up all the sources from a deleted article all over again when new sources surface and the subject becomes notable. When a user asks why a certain subject doesn't have an article, linking to a source assessment (or suggesting the creation of one) can also be helpful.
The idea for this was first suggested on the idea lab village pump (and now boldly created).
For all source assessment pages, see Special:PrefixIndex/Wikipedia:Source assessment/.