In reply to Aleksandar Borisov.

Performance is gained by optimizing bad code, not by adding new bad code to patch old bad code. This WebP conversion will make uploading files slower, will make the database fuller, and your site load longer as it tries to test for browser support.

The benefit is saving 5kb over a single stream, which takes less than 50 nanoseconds on modern connections, a benefit so non-profound that it cannot even be accurately measured. The processing required to make this feature a reality is a thousandfold slower, so your site will be slower thanks to this feature.