The tab Plugin Metrics gives you insight into which plugins use the most memory, and consequently slow down your store. This helps you find poorly coded plugins that are slowing down your store.
Open the tab in your Store Dashboard.
The plugins are sorted by Memory Usage. You should look into possible alternatives for any plugins that use more than 2 MB of memory (excluding WooCommerce).
Variations in memory usage are expected if a large part of the functionality is used only when the administrator is using the plugin.
There might be multiple versions of a single plugin shown. This way you can compare the usage between the old and new versions of the plugin. If the new version introduced an issue that causes more memory usage, it'll be easily seen here.