Largely cultural, I think, and being able to use each as might be appropriate within the culture. For example, using "Hi, <first name>" when sounding casual, bu

Largely cultural, I think, and being able to use each as might be appropriate within the culture. For example, using "Hi, <first name>" when sounding casual, but using "Dear Ms <last name>" when trying to sound formal. Nothing that's likely to be mission-critical, but a natural inclination based on cultural upbringing that we may not even realize is affecting our product design.