Depends on what you're building. Client side rendering vs SSR have both different trade-offs and performance implications, and it's best to evaluate which is better for your use case.
For a blog or mostly static webpage? SSR is probably the better choice. But there are many times where serving a minified React bundle to the client and letting it do all of the rendering work is better. It's actually a much lower strain on your server, because all you're doing is serving static files from behind a proxy like Nginx, whereas with NextJS your server incurs significant performance overhead from having to evaluate each page view in JS. Imagine this for a million visitors at once when you have content that cannot be statically cached.
For a blog or mostly static webpage? SSR is probably the better choice. But there are many times where serving a minified React bundle to the client and letting it do all of the rendering work is better. It's actually a much lower strain on your server, because all you're doing is serving static files from behind a proxy like Nginx, whereas with NextJS your server incurs significant performance overhead from having to evaluate each page view in JS. Imagine this for a million visitors at once when you have content that cannot be statically cached.