Suppose you rollout a new feature and have done internal over haul in application which might have broken some links. You assume your testing team would have thrashed out the issues but that might not be case. How to ensure that all the links and buttons are working inside your application and none of them lead to 404 error ?
You need a tool that runs over your site and checks all of the links.
I use SSW Link Auditor which will run over all your links to pages and images and give you a nice report. The free version works for up to 500 links but if you have more you may need to purchase one of the other versions.