Unnecessary repetition is usually considered to be a bad thing in English. Generally, careful writers try not to use the same words and structures in successive clauses and sentences without a good reason. It is often for deliberate emphasis or other stylistic purposes when expressions are repeated. In informal language, casual repetition is more common, but even in conversation people often sound monotonous or clumsy if they do not vary their sentence structure and vocabulary. In both writing and speech, some kinds of repetition are actually ungrammatical.
We normally use a pronoun instead of repeating the original noun phrase when we refer again to a person or thing that has already been mentioned. Repetition is usually not only unnatural but grammatical, when the reference is very close to the original mention.Some examples:
1. What’s Ken doing here? – He wants to see you. You do not say “Ken wants to see you.”
2. Mom’s just cut herself slicing carrots. You do not say “Mom’s just cut Mom slicing.”
We do not very often repeat a subject or object with the same verb.Some examples:
1. That room needs cleaning. (More normal than “That room, it needs cleaning.”)
2. I saw my cousin yesterday. (More normal than “My cousin, I saw him yesterday.)