Building permits are mainly about safety. They enforce construction standards.
The first reason to obtain a building permit is that it’s illegal not to. If you fail to get a permit for work that requires it, you can be fined or you may even be forced to remove a building or tear out completed work. Not only do they keep your contractor honest and your insurance updated, but they are necessary if you decide to sell your home. The permit process is a matter of public record. If you renovate or add to your home, the new information must match the town tax records. If you are planning a home improvement and not sure whether a permit is required, check with your local building officer.