Multiple domains and Google penalties

Novice Webmasters, but also self-proclaimen SEO experts, are convinced that Google is a kind of executioner, ready to anastomise those who practice "copy-paste" content from sites of others or even from their own. Things are not exactly like this and it is worth clarifying some aspects.

First of all, regarding the duplication of non-authorial content is certainly discouraged by Google (just look at its Guidelines for Webmasters), but keeping in mind that there are different types of duplication and above all that the reasons behind this action are not all the same: those who simply republish a blatant copy from another site for non-syndicated purposes (interest in the subject, but lack of preparation or lack of time to reformulate the concepts, desire to share content deemed interesting and reliable, etc.) is generally not penalised or at least in minimal measures, i.e. by dropping the incriminated page to the last places in the search indexes.

On the other hand, a duplicate content with obvious ranking purposes may entail a penalisation to the entire site, which will be subject to a real "ban" by Google. Another case is represented by duplicate content, which provide more URLs on the same domain indicating the same content: although this practice does not involve any "disciplinary" sanction, it may be not very useful, as it implies a probable circumvention by the Google Spider: wanting to offer its users a certain variety in search solutions, the system tends to filter URLs that have the same content, presenting them in a single cluster.

For those who have multiple domains with the same content, this could have significant implications: Google's filter could in fact hijack users on what for us is the "secondary" domain because perhaps affiliated to a particularly authoritative site, not considering our main domain, where no added value is found for potential visitors. Thats why "playing" with multiple duplicate domains can be counterproductive, especially if our business is based on traffic within our site.