This is a great feature we have added to help you easily optimize your images for the web so that your pages load quickly for your visitors! For more information, see Image Optimization.
The Optimization button allows you to turn this feature on or off on any of your Picture widgets. In general, if the file size of the image is already small (less than 75KB) you should keep it turned off or you will lose quality on your image.
However, if you have uploaded a high res image with a large file size, use the Optimization button to quickly compress the image to the right size. Note: the original image file will always be available in your File Manager if you need it.