A mid-sized business or nonprofit with over $1M in revenue or annual operating budget. You have a team, or people you can bring in, and no marketing strategist on staff.
It works when someone has the authority to make decisions, the organization can act between sessions, and you want a strategist in the work with you rather than an agency doing it somewhere else.
It doesn't work when there's no capacity to execute, or when what you actually want is done-for-you. I'd rather say that on the first call than four months in.