Many WordPress plugins add their own tables to database. A high percentage leave these tables behind even after being deactivated and deleted. This can affect your site performance, so these old tables should be found and removed.
One common complaint is slow admin. Deleting the old tables can often fix this issue.
This great plugin has not been updated in over a year now. It works with the latest WP though (4.8.1 as of this writing) in my own and clients’ experience.
Please make sure to backup your database before using the plugin.
Follow the instructions and locate non-WP tables. They will be marked in red. These entries will also be marked as “Deleted” with a question mark.
The reason for the question mark is because some tables will be named less than intuitively. Please make sure to only delete the ones you’re completely certain belong to the plugins you no longer use. When in doubt, try looking them up.
I’m going to repeat myself and remind you about creating a backup before proceeding.