When you install WordPress for the first time you have the choice to set the preferred domain.
You are offered with various choices of selecting your preferred domain like,
If we take this website http://www.digtizedpost.com for example,
HTTP is used as a protocol to transfer the data for the website. WWW is just and identifier and indicates that digitizedpost.com is a website.
Most users think that WWW is obsolete for modern website. Its not like that it’s just an choice of preference. I stick to WWW because I want to market my website as WWW. For my other site I have used non WWW URL.
Twitter is one of the best example for now WWW website.
I have noticed several websites wont properly redirect when I type domain.com whose preferred domain is set as www.domainname.com. Non technical users will think that the site is not working if it is not properly redirected.
A study tells that most of the people are lazy to type url with www, they will just enter domainname.com. If you use non WWW URL you have to redirect and need to update the google webmaster tools. By updating google webmaster you are telling google to index your preferred domain. If you failed to update webmaster tools both your www and non www url will be indexed and eventually google panda will penalize you for duplicate content.
Which is better for SEO benefits?
There is no significance difference between choosing www and non www version for SEO benefits. It is just your preference.
When you switch to www or non www version make sure the redirection is done properly in .htaccess file
If you want to set the preferred domain do it when you are installing your website for the first time. You can do it later also but there might be chance of losing minor traffic. Also think about the backlinks you have created. One of popular website changed its URL from https://domainname.com to http://domainname.com when their site is popular. When they changed the URL they haven’t redirected the old URL to new one. When a user clicks that back link it gives 404 error. So they have lost all the quality backlinks that they have created. Also if you are a a owner of website and if you create a link that points a external domain you should be cautious of broken links. When the external domain URL is changed, the link that you have created will be a broken link.
How Web Filtering Softwares will look at the change?
Some web filtering tools like Websense will re-categorize your website when you change the URL. The website with new preffered canonical URL will be treated as a new website. Mostly it will fall under the uncategorized category in Websense for a new website. Depends upon the categorization your website might be blocked or unblocked.