Deactivated or inactive plugins do not slow down WordPress. Keeping inactive plugins installed is harmless, but they can be quite problematic at times, as WordPress will still show updates for them and these files can get infected in case of a hacking attempt. Thus it is safe to delete any inactive plugins that you do not intend to use on your site.
WordPress only loads files whose file paths are stored in the active_plugins option in the database, and ignores everything else entirely.
The one caveat to this: if the deactivated plugin stored a lot of autoload data in the wp_options table. This could have a marginal effect on the performance of a WordPress websites, reports some users on StackExchange.
Should you delete inactive plugins?
Yes, if you don’t plan to use them soon and fear that deleting the plugin will delete its settings then they should be kept. Otherwise there is no point in keeping them installed since they can be quite problematic at times. In addition they can also get infected during an hacking attempt so as a security precaution any inactive plugins should be deleted immediately.
Should I delete inactive plugins that I don’t plan to use?
It is recommended that you delete any inactive plugins if you do not intend on using them soon, as they can pose a security risk since they are vulnerable to hacking attempts.
What happens if I delete a plugin without uninstalling it first?
If you delete a plugin without properly uninstalling it, then settings and other data associated with the plugin will still be stored in your database and could potentially lead to issues. It’s recommended that you properly uninstall any plugins you aren’t using before deleting them.
Not all plugins have an uninstaller, and the ramifications of leaving the data in the tables is probably okay.
Is there any upside to keeping inactive plugins on a WordPress website?
No, there is no real benefit to keeping inactive plugins on your website since they won’t be used and will only add clutter. It’s best practice to delete anything that you do not need.