I ran across an example of the importance of having site search on a blog. I was blog surfing, for blogging theory type posts, this morning and found a post by @manton on his blog which linked to an article by @douglane which mentions future articles. How to find those articles? Use the handy search box at the bottom of the page.
Yes I could have done a site search from any search engine, but I’m a lazy sod and why open another browser tab? Anyway, it brought home to me just how important that search box can be to a visitor, who wants to read more of what you have written.