Slack, efficiency, and choice

Slack is the opposite of efficiency. Slack is excess capacity, unused space, extra money. Slack is waste and therefore considered bad.

Yet things are not that simple. Yes, slack is excess capacity and unused space. And yes, slack can be viewed as waste. But slack is not entirely bad. Slack has value.

Consider the recent (infamous) overbooking event on United Airlines. One passenger was forcibly removed from a flight to make room for a United crew member (for another flight, the crew member was not working the flight of the incident). United had a fully-booked flight from Chicago to Louisville and needed to move a flight crew from Chicago to Louisville. They asked for volunteers to take other flights; three people took them up on the offer, leaving one seat as an "involuntary re-accommodation".

I won't go into the legal and moral issues of this incident. Instead, I will look at slack.

- The flight had no slack passenger capacity. It was fully booked. (That's usually a good thing for the airline, as it means maximum revenue.)

- The crew had to move from Chicago to Louisville, to start their next assigned flight. It had to be that crew; there was no slack (no extra crew) in Louisville. I assume that there was no other crew in the region that could fill in for the assigned crew. (Keep in mind that crews are regulated as to how much time they can spend working, by union contracts and federal law. This limits the ability of an airline to swap crews like sacks of flour.)

In a perfectly predictable world, we can design, build, and operate systems with no slack. But the world is not perfectly predictable. The world surprises us, and slack helps us cope with those surprises. Extra processing capacity is useful when demand spikes. Extra money is useful for many events, from car crashes to broken water heaters to layoffs.

Slack has value. It buffers us from harsh consequences.

United ran their system with little slack, was subjected to demands greater than expected, and suffered consequences. But this is not really about United or airlines or booking systems. This is about project management, system design, budgeting, and just about any other human activity.

I'm not recommending that you build slack into your systems. I'm not insisting that airlines always leave a few empty seats on each flight.

I'm recommending that you consider slack, and that you make a conscious choice about it. Slack has a cost. It also has benefits. Which has the greater value for you depends on your situation. But don't strive to eliminate slack without thought.

Examine. Evaluate. Think. And then decide.