The important is choose one and go with it and do not change it, it alters the quality of backlinks that have or will be built if it is switched around. SOme of the engines (there are more than google yahoo and bing) treat the with or without differently, the web was based on www (that is the complete addy...as there are new things besides www.
google leans towards an algo of using www, some sites and bloggres with lots of traffic go without but when you pay attention to how google labels there stuff they always use www when they have their links...and in the wp setting without the www, or with it acts as a redirect...and for example i first set up the xml map on danas ...it didnt have the www...and when i altered the setting to hit www...i went back to the xml i created and it didnt link over ...cause the two things were different..
yes it can be set up to act as a redirect, but if you dont have to do a redirect there is no point to ...its an extra for the browser...and bots..
i know you feel it unecessary, and it looks cleaner without but it helps identify it as a website cause not all sites are .com remember, and a majority of the world types www,
for seo some bots treat www or no www as two different sites so it is important to stick with one approach and the easiest approach is always instinct of www for a majority of ppl, one approach because of future links to be created...strengthen one site not two
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