A common task on the web is converting images such as .png files into other formats, such as WebP.
WebP has often been criticized unfairly for not having full-native browser support until recent times. One criticism that was justified, was the actual filesize savings...
A JPG/JPEG file converted into WebP for example can often offer very little compared to simply compressing the JPG/JPEG.
Compressing prior to converting into the WebP format makes all the difference. In the case above, the total filesize reduction totaled 92.07% when compressed AND then converted.