Apple's HQ campus is an interesting one because it's only a small percentage of their employees that actually work there. I imagine if they downsized their silicon valley properties down to infinite loop and the ring building, they'd still be able to easily fill them up with people who like working onsite, conference rooms, meeting spaces, labs, etc.

I am not personally aware but I do remember hearing they had office spaces all over the place because they don't have enough room on the main campuses for all of the employees.