How Companies Incentivize Layoffs
scarletink.com
scarletink.com
I did it for a few months. It was truly unpleasant.
It does not happen by accident. Both the manager and the reports are usually top notch for the team to be successful. The manager knows how to effectively delegate responsibility (not tasks) and the reports are intelligent, self-driven, reliable and know how to use their network for help and report back to manager when they are stuck.
Best test if the manager is able to have more reports is if he/she can go for 2 week vacation and the team is still delivering. If the manager hoards operational responsibilities then this is probably not going to work well and he/she is not ready to have more reports. To have 20-30 reports you need to delegate all operational responsibilities so that you are not in critical path of any ongoing project.
Over 15 reports, though, you have no choice.
Par for the course is blaming that their team is too large and the team is broken up and they become a director with 2-4 reporting line managers.