Why would I use an em dash instead of a comma to punctuate nonessential information?

Which is the best example of stream of consciousness writing? o a. 1. separate all the individual pieces of the cabinet. 2. using the wooden tabs, join all four l brackets until they form a square frame. 3. situate the frame vertically o b. i have to get out of bed, but it would if i had some reason, like a hot breakfast already waiting for me. come to think of it, cold cereal sounds pretty good right now. o c. while some have accused me of madness, i ask you, is it mad to want what is best for one's country? the welfare of the country is my sole motivation o d. sir bors halted at the edge of the cave and peered in. he hoped for some glimpse of his enemy to him gauge the monster's movements.