Here's why:
* Readability: Capital letters are harder to read than a mix of upper and lowercase. It can be tiring on the eyes and make the letter appear shouting or unprofessional.
* Convention: Standard letter writing conventions dictate using proper capitalization for names, titles, and the first word of each sentence.
* Etiquette: Using all caps can be perceived as rude or disrespectful, especially in formal correspondence.
However, there are a few exceptions:
* Acronyms: You can use all caps for acronyms like USA or NATO.
* Headings: Some headings or titles might be all caps for emphasis.
* Specific Instructions: If specific instructions require all caps, such as in a legal document, follow those instructions.
Always aim for clear and professional communication. Stick to proper capitalization unless there's a specific reason to deviate.