Cognitive cost, or any similar term, is a pretty unscientific generalisation for a range of things that detract from your effectiveness. It has the sound of "Woo-woo" to it, but in fact is not. While it is not necessarily very scientific, it refers to a broad scope of difficult to quantify but readily demonstrated effects on our state of mind including but not limited to:
- Quality or aesthetics of environment
- Demand for concentration
These are all fairly obvious to us; we're not productive if we're being interrupted. If we're in an environment full of distracting noise the 'cognitive cost' is the mental effort required to concentrate compared with a more peaceful setting. These things make The Work harder.
It's also more subtle, like the effort required to find a buried feature in the poorly designed interface of a popular word processor. While it may have been arranged into a menu bar where accessing it only needed two clicks, the frustration and many clicks spent finding out which specific clicks were the right clicks has an impact on the flow and enjoyment of the task at hand. It might seem trivial, but it cost you time and patience; it cost you your focus. That silly little thing selfishly took your mind away from what mattered.
Even our own behaviour can put strain on our mental reserves. Taking a risk requires willpower and confidence, both are renewable but not limitless resources. We know that difficult decisions, challenges, our own insecurities, and phobias all require mental exertion and affect our behaviour afterwards. Learning and practicing new skills is costly; new information needs to be retained and new skills have to be repeated. We know that we need leisure and recovery time if we want to maintain our mental performance.
So what does it matter? Both the quality and stress of doing whatever work you're doing are going to be affected, and while pretty much everything has a cost in this sense it is therefore of real benefit to you to limit the ones that you have control over. Some of these costs are necessary, you know that you're trading the short term difficulty of learning something new for long term benefits. We all know how frustrating it is to have software crash on us repeatedly or how difficult it is to concentrate while someone digs up the road outside your office. You have control, at least to some degree, over your environment, your workspace and your surroundings. You get to choose what tools you use. Removing the distraction and friction makes your job easier, will make you happier, and will improve the quality and satisfaction of your work.