If you are behind on a car loan or a home mortgage and you can afford to catch up, you can reaffirm and possibly keep your car or home. If the lender agrees to give you the time you need to get caught up on a default, this may be a good reason to reaffirm. But if you were having trouble staying current with your payments before bankruptcy and your situation has not improved, reaffirmation may be a mistake. The collateral is likely to be repossessed or foreclosed anyway after bankruptcy, because your obligation to make payments continues. If you have reaffirmed, you could then be required to pay the difference between what the collateral is sold for and what you owe.
If you are up to date on your loan, you may not need to reaffirm to keep your car or home. Some lenders will let you keep your property without signing a reaffirmation as long as you continue to make your payments. Sometimes lenders will do so if they think the bankruptcy court will not approve the reaffirmation agreement.