A debtor has to deal with many Chapter 13 limitations. While in a Chapter 13 the debtor must make plan payments, keep current insurance on collateral for secured debt, and not incur significant new debts without court approval.
The debtor can move or change jobs. Court approval may be required for getting new debt like a car loan, or refinancing or purchasing a home.
Plan modifications may be required with a change of income. The Plan as modified must still meet the tests for plan confirmation.