You can use capital letters in your copy to emphasize something. But you have to be careful. If you use capital letters too much, it gives the impression that you're shouting. It may even appear dogmatic. And that turns off prospects.

I used to visit a local forum regularly where one of the posters used capital letters a lot to emphasize his points. We'll call him SP. SP would post how-to or "inspirational" articles on the forum. (Although this is about a forum, it still has a lot of similarities with sales copy.)

In SP's posts, he would use capital letters a lot by writing a word in all capital letters here and there.

From my point of view, it looked like he was shouting. It seemed as though he was trying to force his opinions down my throat. The tone of his posts was dogmatic. I didn't like it. And from talking to other forum members, they didn't like it either.

He would also talk down to his readers as though they were stupid or lazy. Whenever he talked about himself, it always seemed like he was boasting how great he is. Whenever I read his posts, it always made me feel inferior.

Although he would emphasize his points with capital letters, he rarely gave proof to prove his claims. It was as though the claims he made were true simply because he said them.

I never looked forward to reading his posts because they always made me feel worse afterward. (By the way, in sales copy, you can't win sales by making your prospects feel worse.)

SP started a company later on and created a company blog. He regularly wrote in his company blog for more than a year. But all his blog posts only had a few comments at most, and a lot of them had zero comments. Eventually, he stopped posting in his blog altogether. He removed the link to his blog on his company Web site.

Even after more than a year, his blog was unsuccessful. I'd say that his writing style and using all capital letters was likely a cause of it. (Interestingly though, he's a nice and friendly guy in person. But his writing gave the opposite impression.)

If you want to emphasize your points in your copy, be careful if you use all capital letters. Try using other ways to emphasize your points. You can write in bold letters. Or you can italicize your words. You can also underline them. Highlighting your words with a yellow background is another way.

So instead of using all capital letters, try emphasizing your words using another method if you can.