For example if you have 20 team members and expect for 2 to be gone for some kind of vacation at any point. When all are at work you have a 10% inefficiency.
I wonder if it would be more effective to have have stretches of intense work (4-6 months) with long rest periods (1-3 months) between. This would minimize the operational switching frequency, though it would take longer probably.
Let's assume that no engineer is getting less than 2 weeks of vacation off a year on paper. Most of these articles are written by people giving 4 weeks of vacation. So we're talking about the difference between a 'stingy' vacation policy and a generous vacation policy being 2/52 weeks in the year.
If people gain more than 4% productivity by avoiding burnout, you net win by giving people more vacation. I would argue that net productivity gain from letting people de-stress is way more than 4%, though I have no numbers to back that up.
Expanding on a point by brational, see Tom Demarco's book Slack: Getting Past Burnout, Busywork, and the Myth of Total Efficiency. It makes the argument that if your goal is long-term profitability, you must have some excess capacity in human resources at all times. http://amzn.com/B004SOVC2Y
http://www.everydaykanban.com/2012/07/27/slack-is-not-a-dirt...
I, personally, like your suggestion of stretches of intense work followed by long breaks, but I think that the reality of family life, hobbies, interests, and other commitments make that pretty unrealistic to impose on a team. You'd also have to be very committed to making sure that the work periods are strictly bounded, and it could be very tempting to slip and say "just another few days" / "just another week" and end up working to breaking point.
Edit: Grammar
Most companies probably have 50% of their workforce surfing the web at any one time.
By giving them more vacation maybe?
If someone is only putting in 2 hours of efficient work a day, then maybe you should start thinking about shuffling them within or out of the organization depending on the position and level they're filling, but asking about 10% inefficiency due to "missing bodies" is equivalent to complaining about getting shorted a penny from the barista. It's literally pocket change, get over it.
It's the same way that buying extra hard drives for backups is "inefficient," since you rarely use those drives, but still far more efficient than recreating all of your lost data from scratch.
Surely in a team of 10 developers working on the same thing, if one quits the others can take over the work, just with a schedule slip?
Smart people don't exploit systems operating at their absolute limits.