We've just introduced a new size option to the free low-res "comp" downloads:
This allows you to offer downloads to your clients in sizes larger than 800x600 px. So that the download can be started in a single click, the alternative size is the same as the one used on your website (set via the gallery display style settings).
In addition, free low-res downloads applied to video clips now contain the (potentially watermarked) video itself, either in 360p or 720p size, instead of a still preview image (applies to new and updated galleries).
Free low-res "comp" downloads are a great way to give professional clients access to files they can use in layouts, for example before purchasing the high-res versions. They are watermarked if the images on your website are.