Most image optimization plugins process each photo as it is imported into the media library: they generate all the sizes required by the theme at once,thumbnail, catalog size, product page size, gallery,multiplied by the alternative formats (WebP, sometimes AVIF). This work is done once and for all, regardless of whether a visitor subsequently views that image or not. In a catalog with several hundred listings, a significant portion of these variants will never be seen by anyone: sizes designed for an older theme, formats that most visitors never request, or simply product pages that are rarely viewed.
The true cost becomes apparent when you switch themes. A new theme rarely replaces all image sizes with the exact same values,as soon as a catalog grid changes from four to five columns, or a new product page layout requires a different aspect ratio, all the previous generation work becomes obsolete: the old sizes remain on the disk, useless, while the new ones must be generated,often via a complete new batch processing of the catalog.
ImagePipe reverses the order of operations: nothing is generated upon upload. The first time an image is actually requested,by a real visitor, in the size and format negotiated by their browser,ImagePipe calculates that specific variant just once, then writes it permanently to the disk cache. All subsequent requests for the same size/format/mode combination receive the cached file directly, without recalculation: the visitor who triggers the generation experiences only a marginal delay, which is imperceptible by the time anyone else visits the same image on their next visit.
Direct consequence: changing the theme, catalog grid, or product page layout no longer requires running a batch process on the entire catalog,old, unused variants simply remain on disk until the next cache cleanup, and new ones are generated as actual visits occur, never in anticipation of hypothetical use. A visitor using a browser that does not yet support AVIF will never trigger the generation of an AVIF variant for that image,unlike a batch process, which would have produced it for everyone, including formats that no one will ever request from that specific catalog.