What is a common reason for using washers with fasteners?

Using washers with fasteners primarily serves the purpose of distributing load more evenly across a surface. When a bolt or screw is tightened, it can create a concentrated point of pressure on the material being fastened. This concentrated load can lead to material deformation or damage. Washers help to spread this load over a larger area, reducing the risk of damage to the workpiece and improving the overall integrity of the fastening assembly.

While other options, like creating a seal or acting as a spacer, can be specific purposes of certain types of washers (like rubber washers for sealing or thick washers for spacing), the fundamental and most common role of a washer is load distribution. Decorative purposes for washers are typically not their primary function in applications involving fasteners.