re: Is a Full Freezer More Energy Efficient Than an Empty Freezer?

Very slightly more efficient, yes. Simply because the temperature inside is more stable so the number of cooling cycles decrease (though it has to run longer to cool all the mass back down when the cycle starts). But the heat loss is the same regardless of what is in there so the savings is tiny. The other advantage of being full is it will last longer in an outage. We were without power for a day and a half this winter in a storm and didn't lose anything from either freezer.