Your web site has been up and running for some time now. Everything works as it should, right? It's important to periodically check that all the links on your site (especially ones that go to external sites) don't go to dead pages, and that any forms on your site still function properly.
Links:
If you have links to other sites - those sites may have been updated, may have a new web address, or may no longer exist, so you need to check them to make sure links from your site are current and go to the correct pages.
Online Forms:
Hosting firms may change their policies on what type of scripting is supported for online "contact us" forms, so it's crucial to do a test submission of your form once in a while to make sure that your contact form still works.
