There are two things here, from a legal perspective:
Secondly, many people are unaware that the assertion of copyright by including boilerplate text in the footer adds nothing, strictly speaking, to the protection already offered by law and case law. Thus, if you have a website with original content, your content is automatically protected by copyright. Every piece of writing, music, or artwork is automatically protected under U.S. copyright law, regardless of whether you formally register it with the U.S. Copyright Office or include a copyright notice on it. If your copyright notice fails to deter an infringer and you need to sue for copyright infringement, the existence of the copyright notice will help to establish that the defendant had actual notice of your rights.
Taking away the innocent infringer defense is important when it comes to calculating what damages you’ll be able to collect. For example, when it comes to statutory damages, the court can set the amount as low as $200 per infringement for an innocent infringer, while intentional infringers can be on the hook for as much as $150,000 per infringement.
Having stated that, there were two further considerations that led me on the path described in this topic:
A copyright notice must state the year the work was published. A website is published when it’s first launched. If you subsequently change the content on your site or you reorganize the pages on the site, you can refresh your copyright notice to the year of the update. Thus while almost everyone includes the copyright footer boilerplate using the form you mention, best practice dictates in principle that the correct date or range of dates for each page should be included, and that inevitably requires a conditional if like me, you choose to list a range of years for the year of publication and from time to time updating the year at the end of that range.
Conversely, in some cases content creators will spontaneously want to mitigate the automatic copyright protection afforded by law, and in such cases they often mention this somewhere on the website. I do this, for instance for my articles, as explained in my site terms:
This Creative Commons license is not a substitute for copyright, but exists independently of it, in the form of a license applied to a work that is and remains protected by copyright. It is not separate from copyright, but instead is a way of easily sharing copyrighted work.
It’s true that it’s unusual to see mitigations of copyright included in the footer, but I’ve decided to do this on pages where the content is covered by a creative Commons license, like this one, for instance. In the latter case, as explained above, the Creative Commons license doesn’t waive copyright but mitigate it, so the two mentions coexist, with the appropriate range of dates. For pages where I’ve waived copyright altogether, like this one, the copyright mention is removed and replaced by a link to the Unlicense.