>When making bread in a stand mixer,


Generally
Combine the dry ingredients and dump it into the mixing bowl...
While the machine is running at low speed , add the liquids gradually
until it forms a mass that is either soft or firm depending upon the
type of bread you are planning to make.
Then the mixer speed is changed to medium speed and let it run until
the dough is smooth and elastic...

>>Why?

The simplest answer is ....because that is the way it was practiced
ever since and produced usually consistent results <grin>..