Pronouns serve to make language less repetitive. Instead of repeating what object, person, place, or thing you initially speak about, you can use a pronoun. Without them, many sentences would sound far more awkward and less concise. It would be extremely repetitive to constantly repeat someone's name or an object you are having a discussion about, for example.
Many things use pronouns. For example, the paragraph above used many pronouns. Without pronouns, paragraphs and sentences will sound very repetitive and structurally odd. If someone talks about a man named John, someone would have to continually say John's name every time someone mentions John. As the readers can see, this makes phrases and paragraphs seem to drone on.
(hope this is good!! let me know if you need anything further)
