You have been typing your final year project and it is up to 50 pages before you realise you have been using a wrong word to explain a process or situation. So you have to change this word and replace it with the correct one, it will be stressful to start looking for where you use the word line by line in your write up, instead you just have to find it and replace it with the correct one. It might not even be a final year project or just a word, your boss might just ask you to replace a whole sentence use more than once in a document with another.
To do that, you will need to know how to use the find and replace trick of MS word.
HOW TO FIND ANY WORD AND REPLACE WITH ANOTHER IN ANY DOCUMENT
Find and Replace feature is an icon under the Editing ribbon of the Home tab in MS word. It allows you to search any word or sentence and replace it with another easily.

http://www.techgists.com/2015/06/ms-word-how-to-find-any-word-and-replace-with-another-in-ms-office.html