The major advantage of the newer digital meters is that they are a solid state device, therefore the starting wattage is much lower and there are no moving parts to wear out or get damaged in transit. A newer mechanical meter needs approx 30 watt of load to start the disk moving,(I remember reading GE literature in the 80s, that stated the starting wattage then was over 60 watts.) but the starting wattage for a digital is much lower, down arround 5 watts.
The digital meters are also capable of performing more than just energy measurement as others have stated, the processor allows for per phase measurement of voltage and amperage and easier interconnection to radio, telephone or power line carrier transmitters for data retrieval. Also, as the demand for these meters rose, the cost for a basic digital kilowatt hour meter has fallen below the cost of a Kilowatt hour mechanical meter.
