The {Admin Consent} button is required if you want to use Office 365 authentication.

It has 2 distinct parts:

1) Register and authorize the LinkFixer Advanced Application in Azure to use Modern authentication (required for Multi-factor Authentication and Single Sign-On). This mean the application is registered as an Enterprise App in Azure. 


2) The Global Admin must accept for the organization during this registration. (see attached document) 


Yes, The application has full control, but requires Site Collections Admin privileges to makes any changes.

No changes occur to your sites or files without the accompanying SharePoint permissions as well.

Note: the Global Admin account does not run against your site collections at any point, nor does it grant universal (unchecked) permissions to anyone who uses the software.