What are the security risks/concerns to adding custom javascript to the body of Confluence pages?

[Jeramy]

I have a user who wants me to add custom javascript to the "Custom HTML" section at the end of the Body in Confluence. The javascript hides the create button for a specific space. I've never liked adding custom scripting to the Confluence body or the header. 

What security risks should I be aware of before I allow this change?

Do other Confluence admins allow custom javascript in the header or body of their spaces?

To clarify, I'm not referring to adding this as a macro. They want to use the System-level feature.

Thank you.

[Shawn Doyle - ReleaseTEAM]

I allow it with caveats. I wouldn't give them all the rights to add it, but would add it for them IF I understand the code and they are a trusted source.

You could have them run it through a Vulnerability Scanning tool, several available online, and if Javascript is heavily used in your environment, you most likely already have a standard one.