Glass becomes brittle as it ages and becomes easier to break. In many cases when they try to remove and reset a windshield it cracks/breaks. They want you to know that this is a possibility, and if your insurance will not agree to pay, you will be responsible. The company I used to work for did pay for replacement minus any deductible you may have. If having a gasket replaced is actually what you are trying to do, call your insurance, explain what you are doing and ask if they will pay for the windshield if it should happen to break while the shop is attempting the removal and reset. This is not at all uncommon.