Gesch, D. (2005). Topography-based analysis of hurricane katrina inundation of new orleans. Science and Storms:the USGS Response to the Hurricanes of 2005, 53-56.
During Katrina, aerial pictures of flood areas were not possible yet. Instead, U.S. Geological Survey (USGS) Office of Surface Water used a measure of the water level on Lake Pontchartrain, assuming the flood had leveled out, then compared it to lidar data collected a few years before.
This combination of data systems produced inundation estimates of depth and volume of the flood that allows for a "history of flooding and water removal" to be created. The long and the short of it is, with this information, damages from future floods can be lessened. The effects on certain buildings would be understood, allowing for either fortification or restructuring. And in city planning this would be useful to know where certain measures are needed to improve the infrastructure of the city.
So, essentially, the difference between choosing this home for a likely flood zone or...
choosing this. Which one would be safer? Notice the flood lines halfway up the windows, before choosing.
Another benefit is the experience and ability gained through this technique that will allow experts to provide timely inundation maps for emergency response purposes.