A few things that immediately come to mind: - you can preload the placeholder but still lazy load the full size image - placeholders can be inlined as `data:`

A few things that immediately come to mind: - you can preload the placeholder but still lazy load the full size image - placeholders can be inlined as `data:` URLs to minimize requests on initial load, or to embed placeholders into JSON or even progressively loaded scripts - besides placeholder alpha channel support, it also works for arbitrary full size image formats