It was asked why I don’t recommend using www in your URL for Multisite in WP Multisite 101.
To quote me:
You should not use www in your URL
A lot of people complain about this. The simple fact is that any well built server will automatically redirect www.example.com to example.com seamlessly. By removing it from our install, we avoid any possible conﬂicts with subdomains. Your SEO will not be impacted.
What I didn’t say, but I told the fellow with the question, is that some servers see www as a subdomain, and not an ‘alias’ (for lack of a better term) of example.com, which is my main reason for not using it. I’ve also seen a very rare, but infuriating, problem where, after upgrading, a site that happens to use www in their URL can no longer get to the network admin page, and instead gets a redirection loop. Since this only happens with www in the URL, and never when it’s not, it’s safer to drop the www.
I’ve never yet heard a good technical reason to use it, though I do totally accept ‘But I like it!’ as a justification. Everyone has a preference. I don’t feel that the www makes your site more or less professional, mostly because I don’t think anyone really looks except, maybe, you. As long as the redirect is seamless, the user will never notice, and 99.999% of them won’t care. Yes, Google and Facebook both use the www, though newer sites like Tumblr and Twitter don’t. WordPress doesn’t, but I’ve been advocating no-www longer than I’ve used WordPress.
My technical reasons for not using it stem from the No WWW guys.
By default, all popular Web browsers assume the HTTP protocol. In doing so, the software prepends the ‘http://’ onto the requested URL and automatically connect to the HTTP server on port 80. Why then do many servers require their websites to communicate through the www subdomain? Mail servers do not require you to send emails to email@example.com. Likewise, web servers should allow access to their pages though the main domain unless a particular subdomain is required.
Succinctly, use of the www subdomain is redundant and time consuming to communicate. The internet, media, and society are all better off without it.
To explain what that means, www used to be the protocol to say ‘If data comes for www.example.com, it’s web traffic.’ Similarly, mail is the protocol for email, and mail.example.com sends traffic to your mail server. You could email me at mail.halfelf.org. And the point of all that all web browsers today know that http://example.com is a website. In fact, you can just type example.com into any browser, and it’ll know ‘Oh, this is a website.’ How does it know that? Because you’re in a web browser.
It’s like when you dial a phone number, you don’t have to press a button to say ‘Phone number.’ Look at your cell phone. If you open up your text messaging app, enter a cell phone number, and send a message, the phone magically knows ‘This is a text!’ and sends it. But if you open the phone app and enter the exact same number, it knows ‘This is a phone call!’ You, the user, have to do nothing.
That www in your URLs is telling the browser something it already knows. It’s redundant, it takes up space, and it’s unnecessary.
The main reason I argue for leaving the www. in URLs is that it serves as a gentle reminder that there are other services than the Web on the Internet. Some of these, such as FTP and DNS, users typically use transparently without even realizing it. Others, such as e-mail, users access through separate applications. Even so, I know of many users who will claim with a straight face that e-mail is not part of the Internet.
While I disagree (mostly since, if that holds true, we should use mail.example.com and so on), the question comes up that if we’re not using www, how do we differentiate between http://example.com and ftp://example.com in cases where they’re not on the same server? You can, easily, redirect ftp.example.com to a different IP, if needed, via DNS. Thankfully, there are some easy answers to this. First, you can route the requests via ports. If a request comes via FTP, that’s a different port, send it to the other server. What you can’t do, however, is serve HTTP and FTP over the same port, but … you shouldn’t do that anyway.
There are many personal reasons to use www or non-www, and they are all perfectly valid. But there’s on big technical reason I would never consider it on a Multisite install of WordPress. Once in a blue moon, after an upgrade, someone finds out they can’t get to their network admin. This is, normally, due to a miss-match in URLs, where they’ve put http://example.com and http://www.example.com for their site and home URLs, back before they turned on Multisite. Fixing that is a monumental effort, and it doesn’t always take. (This is probably related to http://core.trac.wordpress.org/ticket/9873 now that I think about it.) Also, even more rare is the case where just having the www forces your subdomains to be subdomain.www.example.com.
Both situations are frustrating. Both are avoidable by using just http://example.com
As long as you redirect the www to non-www, your users will never notice. Except the geeks like me. And while we may disagree, it’s unlikely we’ll stop using your site over something that trivial. Go www free. It’s the way to be.