SSR: Server-side rendering

getServerSideProps only runs on server-side and never runs on the browser. It returns JSON which will be used to render the page. getServerSideProps can only be exported from a page. You can’t export it from non-page files.

Usage

only if you need to render a page whose data must be fetched at request time

If you do not need to render the data during the request, then you should consider fetching data on the client side or getStaticProps