Why do some research centres and university department publish a multi-year future strategic plan?
Another reason may be funding at a large scale. Governments sometimes have plans to strengthen the research in a certain area (ex. biosciences). By making an institution-wide plan, you can make a very strong case for the funding agency and possibly secure a large amount of money. The time scale is also important. If you have money guaranteed for seven years, you can buy expensive equipment and hire experts knowing that you will not have to let them go after a year, for example.

In the particular case of Stanford I imagine their main target is private investment. The aim of the plan is then showing off a strong commitment to their objectives.