A. App-V uses a shared cache, which is stored at C:\Users\All Users\Microsoft\Application Virtualization Client\SoftGrid Client in sftfs.fsd, for efficient use of disk space. If I have 10 users using the same machine, I don't want each user to cache the same program, it would waste huge amounts of disk space.

Even though users share the cache file, users still have to be granted permission to the application before they can access the cached bits of the stream from the file. This is obviously different from when you locally install an application on a desktop, in which case everyone on that machine can use the software by default.