Many events now have timing mats at intermediate points and when this is done they should be measured and placed accurately. The only way we can insure that they are accurate is to certify them and put them on the map. The other day I ran my first negative split in 26 marathons, and I would be quite disappointed to find out that the halfway timing mats were not accurately placed.
The question of recognizing records set at intermediate points raises and number of other questions, as Pete points out. Another question that comes to my mind is gun vs chip times for records as some intermediate points would have to rely on chip times (eg. the 10km between 10km and 20km).