Of course, like all cliches, it did have a use at one time. By the 90s, above-the-line advertising agencies had become so arrogant that they effectively acted as a block on any form of collaboration or innovation.
Against this approach, there was real mileage for those in the market that refused to indulge prima donna behaviour, that had more fluid and collaborative working practices and who were far more open to partnering other agencies.
Some clients, more interested in the process of making work than the quality of the end result, lapped it up.
The trouble is that while there may be some truth in this belief - theoretically, great ideas can come from anywhere, just as, theoretically, a sufficient number of monkeys equipped with typewriters will create works of great literary merit - it is a disaster for clients and agencies alike.
From where are breathtaking strategic, creative and executional ideas more likely to come? My money is on those people who do this every hour of every day of their professional lives, people that instinctively know when something is verging on greatness or just a pile of tat.
Clients: value great ideas, they pay us for great ideas and they stay with agencies that consistently author great ideas. Any agency worth its salt will ensure that, while there may be a scintilla of truth in this hoary old cliche, the greatest ideas only come from them.