Why is it important to pause when writing what punctuation should you use to show a pause in your writing

It's important to pause in your writing because it separates separate thoughts from each other, here's an example:

I went to the fair it was really fun.
 
 With a pause:

I went to the fair, it was really fun.

Use a comma (,) AND/OR Semicolon (;) to make a pause in a sentence.