Why add soda water to beer batter? Why &quot;soda water&quot;, in the sentence above my red heart?

Seafood Basics: 86 Recipes Illustrated Step by Step (2012) by Abi Fawcett,
Deirdre Rooney.
The carbonation in soda water (or beer...or the use of a whipping siphon) is added so that the batter becomes more &quot;airy&quot;, leading to a lighter and crispier final result after frying.