In case we forget, advertising agencies used to be driven very largely by media availabilities. Buyers would visit well-known Fleet Street pubs and negotiate space with the leading newspapers of the day. The question was less about what they paid and more about whether they got any of the restricted and rationed space at all. Then they worked out what to do with whatever they managed to get. The creative teams then had to fill the buckets they were given. Not much has changed really.