If you enter a dollar amount in this field, the program (not you) will determine what years the borrowing occurs and to what extent or how much debt you take on to help smooth your living standard. You do not control the amount of debt you take on with this setting, nor the timing of that debt. You only can control the cap on that debt.
If you are looking for ways to represent school loans or credit card debt, or a home remodel loan, for example, see Loan Repayment (credit card, school loans, etc.)
Setting this $0 amount to something larger can be useful for a plan that cannot run because it is unaffordable. Setting this from $0 up to say $1,000,000 can provide enough borrowing to get the model to run so you can troubleshoot why the plan is unaffordable. Don't forget to return it to $0 after making this temporary change.
By default our software does not allow you to go into any more debt than you already have. By allowing your household to take on debt, you can sometimes borrow against future earnings to achieve a more consistent level of Annual Discretionary Spending. For a realistic plan, only set this number to the amount of debt you are willing and able to take on.