When to use a relative clause?
A relative clause should be used to identify, describe, or give additional information about a noun or pronoun.
Purpose: to identify a specific person or thing:
The book, which I had been reading for hours, was finally finished.
Here, the relative clause "which I had been reading for hours" identifies a specific book.
Purpose: to to describe a noun or pronoun:
The concert, that was scheduled for next month, has been cancelled.
Here, the relative clause "that was scheduled for next month" describes the concert.
Purpose: to provide more information about a noun or pronoun:
The film, whose plot I couldn't follow, was not good at all.
Here, the relative clause "whose plot I couldn't follow" gives additional information about the film.
In general, relative clauses can be used to add more information in a sentence, make a sentence more specific, and make it more interesting.