This subject was suggested by Sue Petryk. All caps is a feature that inexperienced designers often use. Nowadays with all the font choices we have available it is no longer necessary to use all caps to make text stand out. I d encourage you to break. So all caps versus lowercase is a way to contrast type.
Contrast is a wonderful design tool.
Not only are each individual capital letterforms different from its lowercase form, the form of the entire all-cap word is also different. This is what makes all caps so difficult to read. Words that are set in capital letters have a similar rectangular form. We are forced to read the words letter by letter. When type is set in all caps it is considerably longer than the same words set in lowercase.