How to use optimize_database() ?

Hi guys, I have a question.
What use has the optimize database () function? as this function is used?

I was looking for information on the internet but could not find exactly what i need to know. The information in the official document of CodeIgniter is very little

Sorry for my poor english!

Look for information on the 'OPTIMIZE TABLE' sql statement.
That's what the optimize_database() function does.