If your house sits in a flood zone, it is important to document when the water rises to touch the foundation of the building. Many insurance plans require proof of water intrusion, photos are very helpful when submitting a claim to the insurance company. Once the water subsides and the wall dries, it can be more difficult to prove where the water line was if there was damage to the home or foundation during a storm.
Note: I took this photo today after a particularly windy and rainy storm. The owner lives out of area and was sent this, and other flood photos just in case he needs them.