I read about these in one of the answers at Why is godaddy HTTPS/SSL certification so much cheaper than digicert, thawte, and verisign? i've tried googling about this particular topic but can't seem to find much information that describes what purpose does a duplicate SSL certificate serve. It'd be awesome if someone could explain this in simple terms.
What are duplicate SSL certificates?
https;godaddy
The security certificate states that certificate issuer verified the identity of the website operator.   A certificate should only be issued when the identity has been verified and control over the domain name can be demonstrated.A certificate authority may have different levels of entity verification such as:Personal verification for an individual -- check government documents such as drivers license or passportCorporate verification -- check corporation documentsExtended verification -- check the physical presence of the companyDifferent verification levels may be presented to users differently when viewing the website.  For example, extended verification shows a green bar with the company name in many web browsers.To issue a certificate for a domain, they then check that the entity has exclusive control over the domain using methods such as:Registration information matches Website copyright information matchesCan respond to emails at import domain email addressesCertificate authorities compete based on:Reputation of certificate authorityHow thorough their validation is (more thorough is better for users, less thorough is easier for website operators to get a certificate and cheaper to implement).Browser support (are their signing certificates pre-installed in all major web browsers)Ease of useTypes of certificates offered (wildcard, alternate name)CostThe price of digital certificates has dropped in the last few years because discount authorities such as GoDaddy and StartSSL have started competing aggressively on cost.  Older certificate authorities with historically good reputation still charge higher prices for use of that reputation.Most users will never check who issued the certificate.   As long as the browser recognizes the certificate 99.9% of users are happy.