The role of cohesive devices in making a text

Cohesive devices are typically single words or phrases that basically make the text hang together. By analogy, they are much like the seams in our clothing which keep items like jackets and trousers together. Three elementary examples of cohesive devices are word repetition, synonyms and pronouns.
Word repetition
Example: The problem with text linguistics is that it is not easily understood by most people. Text linguistics is a relatively new field in linguistics that necessitates a shift in focus from the word and sentence level to the whole text level.
In the first sentence, the noun group "text linguistics" appears again in the second sentence which is repetition of the same lexical item. This recurrence of the same lexical item adds to the text's overall cohesiveness. It would be incoherent to start talking about something else other than text linguistics in the second sentence.
Synonyms
Example: My favourite city in the world is San Francisco. The capital is world renown for its clam chowder which attracts tourists from all over the world.
In the second sentence "the capital" functions as a synonym for city. Although the second sentence could begin with "city" the synonym used adds word variety to the text, helping the reader stay focused and interested in the idea being discussed.
Pronouns
Example: Baywatch is a TV show produced in America. It has been translated into more than 150 languages.
In the second sentence "it" refers back to Baywatch. It would be redundant to have the second sentence begin with Baywatch.