Every few months someone tells me to serve big images as progressive JPEG. The pitch is always the same: the whole picture shows up blurry right away and sharpens as the bytes arrive, so it feels faster. I had never actually checked what I pay for that.
Source: [Dev.to](https://dev.to/yue_shu_c621a4a637f22396f/progressive-jpeg-saved-me-4-6-and-cost-25x-the-decode-time-61a)