I know about https for securing important pages like login and such. But why would someone create a separate subdomain like wwws as well? for example
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I do this (though I usually use secure.site.com or similar) when I have separate content to serve. I.e., when site.com and secure.site.com contain different things and/or have different restrictions on who (i.e., source IP address) can use them. If they're both serving the same content, then I'm not sure why you'd do this -- I don't see any benefit to it. I'd guess that it was done this way simply because the person who set it up didn't otherwise know how to configure both HTTP and HTTPS on the same domain in the same config.
HP used to do this, and they may still do it. This is how they load balanced their site. Each sub-domain could be associated with a separate IP address and upon logging into www.hp.com you would be redirected to one of www1.hp.com ... etc I think there may have even been a time before CDN's came into their own, that Amazon did the same thing.
Sometimes this is due to poor application design, in which the server hosting website version1 is hosted at 18.104.22.168 (www.domain.com) and then someone rewrites the website because your developer from Texas is now in jail (true story...) and because some XML-RPC logic buried in the pile of crap at www.domain.com is still needed we just redirect our users to wwws.domain.com (22.214.171.124) where our new and improved site is that was developed by Brian the disgruntled ex Microsoft employee.
We aren't sure what will happen if we take down www.domain.com or move it or rename it, so we just leave it instead of migrating our 'good' website back to our primary domain.