Q: Is it enough to deactivate a plug in or should you remove it entirely? 

Asked by Vanessa Kendall at http://claritypaservices.co.uk/

Answer by Pink Elephant Media:

• Do you intend on using the plugin again?
• Is the plugin reliant on another plugin to work correctly?

If the answer to the above is Yes, the answer is don’t delete just make in active.

If the answer is no then we would recommend deleting them.  Inactive or deactivated plugins do not slow down WordPress, so there is no need to uninstall them, however, if you have no intention of using them again we would recommend deleting them as they can cause other issues. Inactive plugins are still executable files and in the case of hacking attempts, which are becoming more common, these files can get infected or can be used to install malware on your website. If you remove them you decreases your threat of allowing hackers access to these files. You will need ensure the server you are on also has safety precautions built in so it can recognise attempts at hacking.

Do inactive plugins slow down WordPress?

The simple answer to this is no. Even if you had 20-30 inactive plugins on your website the plugins will not load (unlike live plugins which will start a loading process when a user makes a request). All the inactive plugins will be ignored and therefore will not slow down the website.
However, live plugins also hold a lot of unnecessary code which can be cleaned so only the part of the code you uses remains. This will improve page speed as well as having good quality servers.