If you are running a WordPress website for a long time you may have installed several plugins now. But you have to uninstall those plugin due to following reasons
Follow the best practices when you uninstall the WordPress plugin
When you deactivate a plugin it goes to inactive state and you can active it again
When you troubleshoot sometimes you have to deactivate the plugin
When you deactivate the plugin it keeps the setting and configuration.
If you do not want that plugin again you have to uninstall the plugin.
If you keep the deactivated plugin in your WordPress website, hackers may use it to run malicious code which can harm your website. So if your website is not properly guarded with a firewall then this will be a major issue for your website.
Shortcodes of the plugin you uninstalled will be visible after you uninstall the plugin. So you have to cleanup those manully by observing your posts and pages.