Churn makes for more efficient companies and stronger employees. When you have 20 year veterans who stayed in a single place for 20 years, you have no exposure as a company to new practices developed in other companies. You have no exposure to what performance level your employees could be achieving. And as an employee, your own skills are not well developed by being stuck at a single place for 20 years.

Churn makes salaries adapt more quickly to market conditions too. That's an advantage when the Fed is dumping capital into the market with QE.

The disadvantage is yeah, there's chaos sometimes and loyalty doesn't exist. But you need some exploration AND exploitation too, else you get stuck at a local minima.