[dngit]

I would argue that the gain is more than "negligible" in some cases. I'm building an app involving storing and serving images and I'm surprised that for the same images with the same resolution/quality, WebP is often 3x-4x smaller than PNG, which translates to lower storage cost, faster serving time, and happier users. You made a good point that people with older devices wouldn't be able to use apps like mine. But for me, the gain is so significant that I might just accept that.

[carlosjobim]

Lowering your hosting costs usually translates into savings counted in the tens or hundreds of dollars per year. Loosing just a single customer because they can't see images of your product means loosing income of tens or hundreds of dollars, depending on what you're selling. Now take that times hundreds, or thousands of customers.

Optimized JPG images are tiny, and will load fast on any device. Any web designer worth their salt must know how to make a performant site without needing WebP images.