Affiliate marketing is certainly helpful for SEO but not entirely necessary. Affiliate marketing is a profit sharing endeavour between an online merchant and the owner of a website. Owners of websites advertise products or services in exchange of shared profits in order to help in selling or promoting the merchant’s products or help to draw more visitors to the merchant’s site.
Affiliate marketing help to build better and more relevant site backlinks but this could also be achieved through other SEO link building techniques.
Its true that few backlinks are generated by the affiliates of a website by they are not generated for a particular keywords hence each affiliate can use his own keyword so one should not remain depend upon affiliate for good SEO rankings.
If you are into affiliate marketing, you can use SEO to optimize your blog or website that points to the main affiliate product. You can get backlinks, do on page/off page optimization and get ranked well. But typically affiliate marketing does not help in SEO, it's the other way around.
Affiliate marketing is an advertising model that works especially well online. It allows advertisers, also known as merchants, to sell their products and services through affiliates, or publishers. Basically, affiliate marketing gives a business a virtual sales force of online salesman, while giving affiliates a way to make money online without producing their own products or services.
A specialized form of marketing where an advertiser seeks to advertise or sell products or services through an affiliate network