If you want more and more people to come to your website, then SEO is necessary. For understanding the significance of SEO, you need to understand what it does for your website.
SEO helps in enhancing the visibility of your website on search engine result pages. Effective SEO brings your site to the top pages of the targeted keyword(s), so that people looking for that particular service or product can see that you too are there offering those services and products. Simply put, Search Engine Optimization is necessary for announcing your presence in the online market and attracting growingly potential buyers for your business.
If there is no SEO for your website at all, it would be like a home which cannot be accessed by anyone because you did not announce its address at all!