If you are looking after a website and if you are in competition in search engines you have to use some SEO tools. There are many free SEO tools and many paid ones. Plagiarism checker tool is the one tool in these tools.
Plagiarism detection process of locating situation of plagiarism within a article or content. Basicly this tool compere your content with the existing content in internet which are already tracked with the main search engines. The full-size use of computers and the arrival of the internet has made it easier to check if an article or content is plagiarized in websites. Maximum cases of plagiarism are founded in copy-paste websites, in which contents aren't really unique. Basicly plagiarism checker tool answers this question "is my content unique?".
Yes it is useful for SEO because if your content is unique and meaningful search engines will love you.
Yes you can find if someone copied your content if they publish it in public network and if a search engine already indexed it.
Here you can find our free tool http://www.fullfreeseotools.com/plagiarism-checker