Duplicate content can harm your search engine ranking and thus you will loose your free traffic. Search Engines like Google love to rank original and user focused content to rank on their search engine. If you are not writing long and original content for your visitors then it will harm your search engine ranking.
Avoid copying content from other websites and pasting on your website. Google is very advance and can easily detect who is copying whom and thus website with original content will rank higher and if all the content on your website is copied from other website then soon your website will be penalized and deindexed from the Google. So, make sure you are writing great content and it should be original.