In its online application form for graduate admission, Stanford University requires three recommenders and allows for another three optional ones. Quoting the application form:
You must provide three letters and evaluations from faculty or others qualified to evaluate your potential for graduate study. At least one letter and evaluation should be from a faculty member at the last school you attended as a fulltime student (unless you have been out of school for more than five years). Substitutions for faculty recommendations may include work associates or others who can comment on your academic potential for graduate work.
Reading this, I feel somewhat uncertain what type of recommendations would most help my application. I'm particularly confused by the phrase
Substitutions for faculty recommendations may include work associates...
I worked for Apple a few years back. A favorable letter from my then-supervisor might convey the impression that I'm technologically minded and enjoy ties to Silicon Valley. Considering Stanford's own proximity and close connection to the Valley, such a recommendation might be well-received?
On the other hand, I'm applying to the theoretical Physics program. My former supervisor at Apple clearly has no basis on which to judge my potential for graduate work in this field. Can anyone provide some pertinent insight into what purpose recommendations are supposed to fulfill? Would a letter solely commenting on my work ethic and team spirit help my case?