Who should be clicking this checkbox?
Salesforce introduced new API end point for authorizing requests for salesforce vendor and technology partners so if you are and existing partner and not a salesforce client you need to click this link. Also you in your API you configuration you will need to add additional endpoint so following
For example
https://odsdashboard.royalcyber.org/openAuthRedictHandler
https://odsdashboard.royalcyber.org/openAuthRedictHandler/vendor