A lot of ad shops dangle digital ideas in front their clients and just figure they will outsource production if the client bites.
But those shops work with their clients in a specific way. They have contracts with their clients that are structured a certain way. At the same time, the best production shops have a very specific way of conducting their own business.
They might be agile. Lean. Waterfall. Whatever. Each of those processes has significant impact on the client's experience, billing structure, how delivery happens, and when delivery happens.
If those ways of doing business aren't in alignment, the agency in between could get screwed. It's so critical to understand exactly how your partners work and how that will affect how you work together.
If you manage your client's expectations from the outset, you look strategic. If you try to manage them after the fact, you look like a moron.