The only use that comes to mind is in emails.
For example:
Hi Jack!
I'm happy to help you out. Just forward me the details, and I can get it done by this evening
Note that this usage is only appropriate when you are reasonably familiar with the recipient, and is usually used by the individual responding to an email.
When in doubt, I wouldn't use this greeting, since it can come off as rude or unprofessional if used with someone of a higher status / with more authority. For example, using it in your first email with a prospective employer may be seen as unprofessional.
Indeed.com describes this greeting as being
most commonly used to start an email because it's direct, polite and personal.