Expense report mandatory accounts purpose and usage

 Hi Folks,

When I check setup check list for internet expenses.

Employee level we need to setup expense account, Financial Options level we need to maintain Expense clearing account?

Where as expense report will pick  Expense account  Debit from  Expense report template

Liability account will pick from financial options.

then what is the use of "Employee level we need to setup expense account, Financial Options level we need to maintain Expense clearing account"  ?