What is the Potential field for in expense submissions?

What is the Potential field for in expense submissions?

I'm trying out Zoho Expense in Zoho Project so I can record project expenses which aren't time related.

On the expense form there is an option called Potential but I don't understand what this is for. When I click the dropdown it just shows the name of 1 archived project for the same customer and nothing else.

Example below.

Is this the right way to record these type of once off project expenses?