Capital letters are useful signals for a reader. They have three main purposes: to let the reader know a sentence is beginning, to show important words in a title, and to signal proper names and official titles.
What does it mean if you use all capital letters?
WHEN YOU WRITE IN ALL CAPS IT SOUNDS LIKE YOU'RE SHOUTING. Using capital letters to indicate strong feeling may be the most famous example of typographical tone of voice. But there are different kinds of strong feelings.