Great interview by John Hegarty, co-founder of TBWA\London in the 70's, co-founder and current chairman of BBH - Bartle Bogle Hegarty to the website I Have an Idea.
Here's some quoting bits:
On ad agencies
"The biggest problem for advertising agencies is none of them act as brands."
On account planning
"We have a fundamental belief that it is all very well having great creative ideas, but if they're on the wrong strategy, what?s the point?
"So ... planning helps us deliver that more effectively and in a more focused way than if we didn't have it. So that's why we have planning."
"It's about understanding and having an awareness of what's going on in the marketplace and having a more acute sense of consumer trends and being able to implement it into our strategic and brand thinking, so that we can then create the kind of advertising that makes a difference."
On the clients
"(...) when they're selecting an agency, it isn't about looking at a wall of ads and going, 'I like that one so I'll go with these people.' It's about getting clients to understand, that here are a group of people that I can have an intelligent conversation with and who really are beginning to understand my business and who can therefore produce, once they've understood my business, some outstanding creative work."
[Via: I Have an Idea]