Users appreciate that the Smush plugin is easy to install and use, providing significant benefits to site performance by efficiently optimizing images. It simplifies image compression, resizing, and bulk optimization, which conserves time and site resources, and improves page load times. Features like automatic compression and comprehensive reports are particularly favored. However, some criticisms include difficulties with customer support for free users, issues with image restoration, and problems on certain hosting environments. Advertisement intrusions in the WordPress dashboard have also been noted. Despite these drawbacks, many users find it a reliable and effective tool for image optimization on WordPress sites.