Not works as expected

WP SmartCrop fully supports both custom thumbnail sizes and default thumbnail sizes. Your issue may be related to trying to use SmartCrop on a thumbnail size that is set to hard crop to specific dimensions. SmartCrop needs the full image to work with, so it falls back into a compatibility mode when used with hard-cropped thumbnail sizes. This compatibility mode regenerates the image on your server to keep the focal point in view, rather than cropping in browser, as we can with images that are not hard-cropped.