You don’t have to document to get the insurance, however, it makes making a claim much easier.
My coworker’s house burned down last year. She had to salvage what she could, they questioned her and her family to see if their descriptions matched. She said an agent also questioned her friends and extended family to see if they would agree that she had owned what she said she did. Not just big stuff either, her mother was questioned over a Precious Moments figurine collection. They looked at other family members’ photos of her house and contents. She says she will always make a video now, it was quite traumatic to have to prove every little thing while trying to deal with the loss. Making a video makes it easier for everyone involved.