There must be a critical mass of controllers in an organisation. Once you drop below it permanent flow restrictions could be in place for a number of years.
The less experienced at the coal face the more difficult training becomes and with system upgrades the experienced controllers required for development and new system training - things could get critical very easily.
Not allowing for the people who move to greener pastures as things deteriorate.
One thing I observed over the years is that training can be the weakest link. The positive - strict flow regulations might make the training OJT easier.