Why not? It's a fantastic system for creatives. They get to take their ideas and make physical product that serves their purposes even better than a CV - it not only says something about them, but provides a real demonstration; "if you hire me, I will basically give you stuff like this for money".
Just how did such a system come about? Necessity, I'm guessing. They can't go to an agency they want to work for and say "I have a level 3 in creativity, for here is my certificate". The portfolio is the solution to the problem of selling ideas.
But what does a planner sell? Well, ideas. So why not a portfolio for them?
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These are the thoughts I had when I started to make my own book. Or perhaps that stuff above is what planning does best, some juicy post-rationalisation. All I know is that creatives got to carry cool books around with them that meant a lot to them - said who they were, what they did. And picked up chicks. I wanted one.
Thankfully, an art director with a vision and some serious Quark skills (mad props, Shwan) agreed it might work, and helped me out - and so , when it came to interview time, I had evidence of my thoughts to show. And something enticing to leave behind, after I'd left.
Did they read it that much? I don't know... but it was a good conversation piece - and more than that, it helped me realise that yes, I can think of interesting things and talk about them. And yes, I might be right for this business.
It's all in the book.
*fictional. But I wouldn't be surprised!