Are you blocking the Wayback Machine from your websites? If you plan to keep the website long term, you may not want to do that as if someone was to copy the content from your website to use on their site, you could actually go to the Internet Archive and show how long your content has been there to prove your case.
Second, if you are not using a Content Management System for your site and is making the pages individually and loose a page by accident or by vandalism, you can go back and grab a copy or copies should you not have a reliable backup to restore from.
If you will not keep a domain forever, go ahead and block it. If you don’t, once someone else grabs the domain, they will retrieve the info and will be able to restore the site with ease. Also, visitors who were not visiting for a while will not know that someone else is in control.
