Why in google webaster or any other website checker tool it is very important to have domain names with www or without www. Does it make a difference? I know we can add ro remove www to website using the .htaccess file, but how it affects seo though?
I also have the similar question and I have asked it on DP, but nobody answer it. awaiting for the answers still.
Having a preferred/canonical url helps in site SEO, and this has been documented well in Google Webmaster forums. For instance, www versions of your site's urls can be taken as duplicates of the non-www versions if you don't set a preferred url.
Do avoid duplicate websites we have to get ride of either www or without www. you can get your other page redirected to the correct URL.