Flour and water... at which temperature? What is the difference between adding hot, lukewarm or cold water to flour?

EDIT:

I'm curious about the following dishes, they all call for flour and some water and I'm not sure how warm the water should be:


Pizza dough
Flour tortillas
Quiche crust
Pizza Dough is usually a yeast bread so you want your water to be warm (100-110F) to activate the yeast without killing it.

Quiche crust, like pie crust, develops the best texture when the flour is mixed with the butter (or shortening) in a solid state, so you want to add other liquids at a cool temperature to prevent melting the butter to a liquid and creating a less flaky crust. 

I am not really sure about tortillas, but with the first two examples you can see that temperature is important and differs from application to application.