The Culture of Long Agency Hours

Coming from the Agency world, I was always perplexed by the long hours people spent at the office. Don't get me wrong, I am all for a long work day and have no problem staying till the wee hours of the morning (2 am during planning season) until the team is satisifed, but to see it being done on a consistent basis never sat right with me. Do we need to spend 14 hours a day talking about a handlful of slides in a deck being presented to the client? Pick your art, get the information in there, and get out of the office. The crafty and unique "purchase funnel" being created to illustrate your strategy is not going to sell the client...the strategy is going to sell the client.  The Digiday article (link above) does a good job of explaining this obscure culture that agencies have opted in our industry. Perhaps it is all driven by billing and revenue for the group. But at a certain point, it seems inefficient to me. What are you accomplishing after 11pm that you couldn't do at 11am?  What are your thoughts?