Distributors want O&E insurance from film producers as a buffer (the insurance company is the buffer) in case of potential lawsuits. It’s Standard Operating Procedure whenever someone gets distribution for their film. That’s one reason you need a “Rights Book” — the insurer will want to make sure you have all your clearances (all copyrights, radio in the background, Simpsons on the TV — anything that shows up in the film must have a clearance).
If you distribute your own film, you probably won’t require all this stuff from yourself <smile>. But it is important to have your “Rights Book” up to date just in case someone comes after you for copyright/trademark infringements.