Salt is of course very important in a dough. There are several proteins in flour that together form the gluten network during mixing. Some of these proteins are more soluble in salt water than fresh water.

Therefore, addition of salt helps to form a stronger gluten network.

Commercial bakeries often add salt at the very end of mixing because it keeps the dough loose so that it will develop more quickly and also does not inhibit the yeast during that brief period. Bread, however, can be made perfectly well without salt.