What file access problems does the "You are about to change permissions on the root directory of the startup disk..." warning refer to?

Question

In an AD environment as a local admin to a server, I went to give a colleague full permissions to a drive (right-click the drive, Security, Edit, add him and give him some rights) temporarily while waiting for him to be added to the correct AD group, and got this warning:

You are about to change permissions on the root directory of the startup disk. This can reduce the security of your computer and cause users to have problems accessing files. Do you want to continue?

I get the first part (security), but what is "cause users to have problems accessing files" talking about? Is that a catch-all in case the change I'm making reduces someone's access to the drive, or...?

Answer 1

I think it means user with full permissions of hdd will also has read permission on all file on that hdd, this may consider as insecure. The user can also change some permisson on files on that hdd so other users may not able to access them. This situation can consider like give someone sudo permisson on linux.