> Why? Who needs this? I don't even understand the use case for file permissions on an external drive.
Shoving data across operating systems using USB sticks or drives is a pretty standard thing to do, at least in the corporate world which is filled with slow internet connections (in related words, never underestimate the bandwidth of a truck filled with SD cards), and particularly when having to send data to clients or vendors.
The fact that there is no standard that works on all three major OS families and in the best case also supports encryption is maddening - macOS has Filevault, Windows has Bitlocker and Linux has LUKS, and neither of the three can understand any other.
Just ask an IT helpdesk in any major company how many questions they get a day by people who have to transfer files to a vendor or client, with encryption. Extra fun in anything involving creative work because most of that happens on Macs whereas most big-corp customers use Windows because of Active Directory and GPO. (And no, ZIP isn't an answer because Apple's built-in unarchiver routinely gobbles up when encountering password protected ZIPs)
> I don't even understand the use case for file permissions on an external drive.
Unlike Windows which conveys the fact that an executable is an executable by the file suffix .exe (or .cmd/.bat, and I think *.js was at least until Windows 7 associated with the JScript interpreter), Linux and macOS do so by using the execute permission on the file.
The use case would be to copy a Java application, let's use jadx, downloaded and extracted on a Mac, then copy it via an USB stick or a Windows CIFS file share on another Mac or a Linux machine, and have the command bin/jadx-gui still start up the UI when clicked upon. As soon as any non-Unix filesystem is in the copy path, it gets inevitably nasty.