Sometimes, links get broken. A page is deleted, a subdirectory forgotten, a site moved to a different domain. Most likely many of your blog posts contain links. It is almost inevitable that over time some of them will lead to a “404 Not Found” error page. Obviously you don’t want your readers to be annoyed by clicking a link that leads nowhere. You can check the links yourself but that might be quite a task if you have a lot of posts. You could use your webserver’s stats but that only works for local links.

I have been using this plugin on one of my blogs for about 3 months.
Done an excellent job of removing scads of dead links.
Yes, it took me quite some time, as I just did not want to unlink or remove links...so I checked links, etc.
But now?
Today, I got only 6 bad links found (weird it actually found 6 after all I had removed).

Broken Link Checker for WordPress | W-Shadow.com