The easiest of embedding outside content on the web page is through iframe – you can just write a line of code and location of the outside content and it will be visible in the web page of your website.
Since, all are up to SEO things – so you need to care where you want to use the iframe and where to not.
iframe is not at all recommended for SEO – because it does not have anything of his own – iframe usually works on the outside content which is not present on the website or it works on getting the content from other folder.
But you know the iframe works on embedding content – and it does not have any name for it – like the page url – iframe does not have page url – as it has different url of the page and the content might be different.
For SEO – you need to have a precise page name and the content should be written in the web page and not in the iframe. As search engines ignores the iframe – as bots are configured to crawl the page content and you might understand that iframe does not have content on the page it just has the link to the content page.
Therefore, if you are keen for the seo and want to raise your search engine ranking – using of iframe in any case is not at all recommended. As you might have unique content but it might not be recognized because of iframes.