What would result from not adding fat to pastry dough?
You'd end up with something somewhere between unleavened bread, pasta &amp; laminate flooring, depending on what else you did with it.
The first two are what you'd get if that's how you treated them, the last is what you'd get if you thought you were going to get shortcrust pastry ;)
Late edit
This started out as one of my more flippant short answers, but has since hit the HNQ* list so naturally falls under more scrutiny.
The point of the 'flooring' aspect is that simple flour &amp; water can be used as anything from wallpaper paste raw, or heated &amp; dried as 'hard tack' which really is hard enough to break your teeth.
Pasta can also be made this way, you can omit both egg &amp; oil, then dry it. Try eating dried pasta without re-hydrating.
Of course, such as chapattis are also made simply with flour &amp; water (a splash of oil is optional) This, rolled &amp; dry-heated is of course, absolutely delicious - so it's the treatment after mixing that determines the end product… &amp; its actual edibility.
What you will never get from omitting all fat is pastry… &amp; we're back round to my flooring joke.
*Hot network questions - in the side bar on the right.
From Comments (Thank you PLL) - Glen Baxter said it best (even if he had a different flour in mind)