I'll argue though there is a political and ideological dimension to queuing theory, especially when it comes to systems where humans are handling the work.

In the idealized case the comfortable place to operate a system is with around 2/3 utilization, like around there latency (customer experience, employee experience) is reasonable, slack is reasonable, etc.

A manager who is being managed by a manager who is being managed by a manager who is being managed (...) is going to see 0.99 utilization and want that last 0.01 and be oblivious to the fact that the math says the system is already past the breaking point, customers are furious, employees are worn out. Any slack at at all seems like an affront.