What are the drawbacks of a website which is not redirected with www ?
how it affects the seo for non www website ?

Its called 304 redirect,

No its not Hurt SEO . even it will help your website It speeds up loading times on clients browsers.

I guess its best practice to have WWW .redirection .

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.