A disproportionate amount of the discussion about Agile in the technology industry centers on product development. However, services are an inevitable part of the Agile story. Here are a few examples:
Consulting teams have to adapt to rapid iterations of new core technology. In other words, the professional services arm has to keep pace with the product development team.
Services are a source of value that gets folded into the product. For this process of productization to work at all, the consulting and development teams need to speak the same language, share common expectations about development processes and deliverables, and work at a similar pace.
Agile consulting teams have to work with customers who aren't conversant with Agile. You might be excited about working at an Agile pace, but your client may have no idea what you're talking about.
That last scenario is a common source of frustration for clients. In place of dense project plans, clients often get a sketchier picture of how the project will proceed. Of course, both client and customer know that, the more complex and detailed the project plan is, the less likely it is to accurately predict what's going to happen. As mythical as the project plans can be, there's something reassuring to clients about having them. At the very least, they provide leverage when the consultants don't deliver.