Ask HN: How do you use internal project codenames in your company?

From what I see and hear, here and elsewhere on the internet, it seems like a lot of companies use internal usage only codenames for the projects they're working on. I guess that's for the sake of practicality and ease of communication. But I've never been in a company that uses one. Now that, at my current job, I'm involved with many projects, I think it's time to introduce the idea to my teammates (and the rest of the company). But, to be honest with you, I have no idea how it works. Do people use them for 'official' communication, in emails? or just as placeholder name for marketing material? etc. I looked around the internet, but no such knowledge was shared before. Can you help me?