A well-organized site lets one find what one wants, and what one didn't know one might be interested in... all those "category" links on Wiki sites like Wikipedia but also IMSLP also, in my case...
Also, finding items related to items one already has, owns, what have can be a particular treat (I have a recording of some pieces but wasn't at all expecting to find scores of them at IMSLP; it's nice to "read along" sometimes, if sometimes difficult still. And some of the books they have at Wikisource are rare enough.)
Surprise can - sometimes - be particularly pleasant :)
