Question

what is the use of find and replace option

Answer 1

if we want any thing in a big passage or any thing find is used
if any mistake or any thing you want to change replace is used

Answer 2

The find and replace option has many advantages.

It can be used in case the user has made some mistakes repeatedly in a very long document.

One can use the option find and replace in such cases to find all the mistakes and can replace the mistakes with the correct words.  

Ctrl + H is used to do find and replace action.