What is the difference between the two Manager Preferred options in the Default Display Currency?

Summary:

The client wants to know how and when does the "else" work between the "Manager preferred currency else local currency" and "Manager preferred currency else corporate currency".

Content (required):

Setup of currencies:

Manager preferred: USD

Corporate currency: EUR

Employee currency: HKD, GBP

When the setup is "Manager preferred currency else local currency" it displays USD in the plan and summary table, the same with "Manager preferred currency else corporate currency". How and when does the "else" work?