If nothing else, being a PM in an agency environment is about achieving balance. I'm just going to skim the surface of this topic in this posting. There are a myriad of competing forces to reconcile along the development continuum in order to find the win/win including:
Reliability & Innovation
Options & Recommendations
Breadth & Depth
Effectiveness & Efficiency
Client Goals & Agency Goals
Collaboration & Autonomy
IM & Email (or picking up the damn phone!)
Revenue & Profit
Branding & Response
Engagement & Accessibility
And the PM classic: Quality, Speed & Price
On the PM side, whether we're talking about employing a service delivery process, using tools & templates or just how one manages communication and relationships, it often comes down to balancing rigor and flexibility.
PM is a robust and mature disciple with a successful history in a number of complex industries. However, an agency environment, is not a construction site, a military base nor a software engineering firm. Many of the PM tactics, tools and tenets that drive success in those environments will choke the life out of an agency. Applied with the right sensibility and professional judgment the methodologies promoted by PMI, Prince2 and the like can absolutely enhance PM and overall agency performance. However, without the appropriate judgment to achieve balance between the rigor supplied by those approaches and the flexibility that must exist in an agency, a clash or a lose/lose is inevitable. Similarly the lack of predictability that comes along with iterative approaches, like Agile is sometimes too nerve-racking for clients or agency stakeholders to bear.
A PM who can effectively depart from a plan to the mutual satisfaction of all is far more valuable than one who can create a 700-line project plan and hold a team hostage with it.
Bend so you don't break.
Bend but don't bend over.