After working client side for over a year I felt that gaining greater understanding of how an agency works from the inside would not just make me a better client but make me a better marketeer.
I spend several unpaid months at RKCR/Y&R London working on accounts such as Bacardi, Virgin Atlantic, BBC, Volvic and GHD. Learning and understanding what goes on behind the scenes, from the inside out, at one of the worlds most successful creative agencies.
This knowledge helps me to squeeze as much creative and strategic ability from any agency that I have worked with and the understanding of the client/agency/supplier dynamic has been applied extensively in my later work.
I would advise anybody else who works client side to try and spend some time agency side. The insight is invaluable.