There are a few different reasons to file for Chapter 13. Probably the first one is if you are not qualifying for the Chapter 7.
The three common triggers for bankruptcy are unemployment, medical expenses, and divorce. Unemployment can trigger bankruptcy, which is pretty straightforward.
The trustee has a duty to conduct due diligence, and that basically means reviewing the documents that are filed by the debtor and then holding a hearing called a Section 341 hearing in which the trustee asks some standard questions of the debtor.