Users appreciate the WordPress Smush plugin for its ease of use and efficiency in image optimization. They like features such as effortless optimization, bulk smushing, automatic compression, and the ability to resize images. The plugin effectively improves site speed and performance, often helping to reduce hosting space needs. However, some drawbacks include issues with image compression failure, lack of support for multisite setups and certain hosting environments, problems with restoring images post-optimization, and intrusive advertisements within the WordPress dashboard. Despite these challenges, many users find the plugin beneficial and continue to use it consistently across various websites.