In the end, this is all about respect for your recipient. If you’re offering a real solution to a real problem, people want to know about it. By following proper and well_understood formats and keeping your writing clear and engaging, you’re making it easier for them to solve their problem. Provided that you’re honest and have the skills and talents to back up your claims, writing a good, solid letter makes it more likely that both you and your reader will be satisfied. Try it the next time you have to write an important letter.
Anything that you'd use in an informal communication is inappropriate for a business letter. This includes slang, text_speak, emojis, and anything off_color or casual. If you're used to communicating mostly with friends, family, or even co_workers you've worked with for a long time, an appropriate closing for a business letter will probably feel pretty stilted at first. Don't worry about it – your colleague or business associate won't feel that way when he or she reads your correspondence. What seems unnatural to you will feel respectful and polite to the recipient.