Oh, how many times have we seen people DO THIS SORT OF THING online? Yikes! Why are you screaming at me? I beg of you folks, learn when you should and shouldn’t use capital letters. That caps key isn’t meant to always be down!
I think everyone knows that all sentences are supposed to start with a capital letter, except in the very rare cases where the sentence starts with a symbol or number. (13 men came into the room.) Proper nouns are also supposed to be capitalized, like Mary Jones or the United States. Those are the easy ones.
Typically, acronyms (words made from the first letter of several words) are also supposed to be capitalized fully, such as NASA or PETA. Some have mixed case like SoHo, but not as many.
Where people go crazy is when they’re trying to show emphasis. By proper writing standards, you should not use all caps for emphasis. “You KNOW what I mean” is incorrect use, but “You know what I mean” or “You know what I mean” are correct. All caps for emphasis became popular on the internet where formatting text was impossible. Writing a word or phrase in all caps was considered yelling, and still is. If you put a word in all capitals, realize that your reader will see it as you screaming at them. Use bold or italics when you need emphasis, or asterisks (*) to draw attention.
Another problem is when people try to claim the use of all caps as a writing style. It’s not, it’s just incorrect. I’ve never encountered anyone who liked reading all caps. It’s difficult on the eyes and makes the writer look bad. On the flip side of that are the people who consider using no capitals at all as a style. Again, it’s just incorrect. Writing style is about the words you choose and how you use them, not violating all the rules of grammar and spelling.