When I insert a link to existing content on my site, I often try to use the Search box under "link to existing content" but it sucks. I can search for the exact name of the page I'm looking for, and it will be nowhere near the top of the results, or not there at all! I don't understand how it works, but it does not work well.
When I search for a page/post to link to, I expect the page I'm looking for to show up in the search results when I search for that exact page name, and I expect to see it at the top. I might also expect the results to be in some kind of order (like, I don't know, alphabetical?) so I can easily find the page I'm looking for. Speaking of which, even when I don't put anything in the search box, the list of pages/posts doesn't appear to be in any kind of order. If they were, I might not need to use the search at all! Instead it shows "recent items" which just isn't very helpful unless I'm linking to the same page over and over again. At the very least, I should be able to sort that list by post date or title. Or maybe choose whether it searches the page/post content or just the title (I'd wager people are generally looking for the title, not some content in a page).
Here's an example. I have a page called Contact. When I search for "contact" in the Insert Link search box, the page titled "Contact" is the 25th option in the search results! How in the world is the page called Contact not the first page that shows up when I search for that word?
In summary, your Insert Link to existing content box needs work.