Most teams think the answer to "we need design" is "let's hire a designer."
It usually isn't.
Hiring is slow, expensive, and permanent. Your design need almost never is. You need a landing page that converts now. A product flow shipped this sprint. A brand that doesn't look like a side project. None of that requires a full-time headcount sitting in your Slack for the next three years.
That gap is what design as a service fills.