Do you know when to scale up (or implement) marketing operations at your firm?
If you try an Internet search for this answer, you are going to find responses that have revenue milestones associated with it. In the AEC industry, those milestones don't make sense.
Those Internet responses typically come from the tech world. That industry generates revenue in a different business model than the AEC industry.
The actual answer for the AEC industry is based on how many people are generating business development activity for your firm.