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Enabling HTTP/2 alone can have a significant impact on your site’s performance, but additional best practices such as gzipping assets ensure optimal load times.Static files such as CSS and JS should be compressed by the server before sending them to the browser. This can reduce file sizes by up to 90%, which can significantly reduce the time it takes to download each asset.

Concatenation

In HTTP 2.0, concatenation isn't required anymore to improve performance. We can now send (potentially) hundreds of requests in one connection, so we don't have to bundle files together anymore. Concatenation was a way to cheat the 6-connections-open-at-one-time limit. That limit doesn't exist in HTTP/2. In fact, concatenation could be counter productive--what if you're loading a bunch of CSS that doesn't get used on a some of your pages? You're just loading extra bytes and that can slow down rendering of your page. In HTTP/1, it was often worth avoiding an extra round trip, but in HTTP/2 it probably isn't.

Further reading: https://deliciousbrains.com/performance-best-practices-http2/

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