In an ideal scenario, you want your employees to be fungible. You don't want any irreplaceable individuals who hold the entire organization hostage. One way of defending yourself from such individuals is ensuring that all members have enough knowledge to take other people's roles, at least after some brief training. The problem is, maintaining high level of competency and transparency is very expensive. The other solution is when your organization is a complete mess and nobody knows what they're doing anyway. Yes, this results in your organization being inefficient, but this inefficiency might actually be cheap in the grand scheme of things.