Bulk Resize Media automatically resizes huge image uploads and makes sure the maximum upload size is respected for all uploaded images.
WordPress creates multiple image sizes, but keeps the original image, no matter how big it is. So you still get the massive image on your server and can include it in posts, which can drastically slow down your site.
Works with Multisite to allow site admins to control the image uploads.
Can be run before exporting to help images make the trip during import.