What is Unique Content and what are its Benefits

We have read frequently about the necessity of having unique content to get traffic. This Unique Content is as opposed to the duplicate and copied content available at other places on the net through free articles or Private Label Rights (PLR) Articles. This is correct that the Search Engines recognize unique content in order to index a web page. Subsequently, the quality unique content web page gets a ranking on google and other search engines. Duplicate content or copied is ignored and even penalized by search engines. What is the Unique Content after all?

Does it mean that only the text should have different words from available text on other sites. In that case one can simply change the words here and there from the articles available on some good sites and place it in one's own site as unique content. This is also being done by some webmasters through re-writing of content. Some softwares (article weavers) are also available which can in minutes produce hundreds of versions of an article each of which can be considered to be unique. Technically, it may be correct as the search engines may consider each version of article as unique. But the main idea behind of each of such versions would almost be the same. So, the essence will not be unique. If the essence is not unique, it is not useful to the viewers who in the course of time will understand it and neglect it. Therefore, in order to attract visitors, the content should contain some unique ideas or planning or at least if the same ideas have to be presented, they should be presented with a difference. Now a days the presentation has its own value. But this presentation can not be changed merely by putting different synonymous words for an existing text. On has to take some pains and give a conscious thinking to achieve it.