Why different coil power versions for a relay?
Most relays are offered in just one coil power version, with a choice of coil voltages. This one seems to be an exception. Most of the time you'll want the most power-efficient part. Possible reasons for choosing the higher power version:  


Vibration and shock resistance. The higher power will pull harder on the contact's anode (the moving part), so it won't open that easy when it vibrates.  
The stronger pull on the contact's anode will probably also result in a slightly lower contact resistance, but I'm not sure how much difference this will make.