The latest Cook's Illustrated addresses that practice.  In a
nutshell:

Apparently if you put enough water* into the dough to roll it
out easily, it baked up tough, too much gluten was forming.
They needed a way to tenderize the finished crust without
reducing the amount of water.

*8 tablespoons

The article said the many recipes say that a teaspoon of
vinegar or lemon juice (in other words, acid) can tenderize
the dough, claiming the gluten formation is inhibited at lower
pH values.  However, their science editor says that isn't
true until the pH drops below 5.  Accomplishing that led to
an incredibly sour crust.

So what they needed was something that is not water but is
still wet, to replace some of the water.  Answer: Vodka.
4 tablespoons each water and vodka.

nancy