Enable RAW Rendering: check this box to render RAW previews. This is helpful if you have made changes to the RAW files in other products, such as Adobe Lightroom®. You can either use the Built-in Renderer or Adobe DNG Converter. If you choose to download Adobe DNG Converter, you need to specify where the app is located on your computer.
Render Cache size: If you have a large drive with available free space, you may increase this number, especially if you use files that are slower to render, such as HIF. Your preferred settings depend on your workflow.
Remove cached files that are older than ___ days old: use this checkbox to specify how often you want to purge old files. If you use a larger cache size, you may want to do this more often to avoid filling your drive.
Empty Now: Clear the cache now. This deletes the render cache and does not delete any photos.