Centuries ago, when bulk transportation was expensive and raw foods were at risk of loss to spoilage or pests, distant farmers might prefer to convert sugar-bearing grain and fruit into ethanol, distill it to concentrate it, and transport that concentrate to distant markets. (This fact was a primary cause of the Whiskey Rebellion in response to the imposition of a tax on distilled alcohol.)
I was surprised at how much more efficient ethanol is as a source of energy, even though energy is lost through fermentation! The chemical equation for fermentation of sugar (glucose chosen here) is:
C₆H₁₂O₆ (glucose) → 2C₂H₅OH (ethanol) + 2CO₂ (carbon dioxide) + Energy
Considered by weight: For every kilo of glucose fermented, we get half a kilo of ethanol and 300 calories of heat (which is typically wasted). But ethanol is more energy dense than sugar: Humans extract 3700 calories per kilo of glucose but 7000 calories per kilo of ethanol! I.e., the metabolic energy available in a kilo of sugar is mostly preserved when converted to alcohol, but its weight is cut in half.