Under which circumstances should multiple projects be grouped in a program?

A program is defined as a group of related projects, subsidiary programs, and program activities managed in a coordinated manner to obtain benefits and control not available from managing them individually. The key criterion for grouping projects into a program is the ability to achieve organizational goals and benefits that could not be realized by managing each project independently.

Having the same project manager or organizational unit is a logistical similarity, not the basis for forming a program - programs are defined by shared benefits and objectives, not shared management.

Having the same scope, budget, and schedule describes identical projects, not a program - programs contain related but distinct projects each with their own scope and schedule.

Coming from the same organizational unit is an administrative grouping, not the defining characteristic of a program as described in the PMBOK Standard for Program Management.