At the beginning of an article or webpage, a functions as a miniature version of the document, giving readers all the key points while skipping over details. this compositional mode can also function as a review, reminding readers of the key points they've just read.

A summaries functions as a miniature version of the document, giving readers all the key points while skipping over details. 
Summaries is created in order to give a potential readers some brief pointers about what the articles is going to be about so the audience could determine whether reading the article will be worth their time.

It allowed for things to be produced much more quickly and efficiently 

Was giving by lincoln on march 4, 1865-as lincoln prepared to speak, the civil war was drawing to a close-lincolns address of 703 words was the second shortest inaugural address-lincoln mentions god 14 times-505 of the words were one syllable -he used the word "war" or it's pronoun 9 times