It sounds a lot more nuanced than a simple 'goodbye'. What subtle feelings or emotions does it encapsulate?
As far as I know it is not commonly used. In fact it sounds so unusual, it was used as a salutation in the 1993 science fiction movie "Demolition Man" (Sylvester Stallone and Sandra Bullock), where people from a sanitized and pacifist future reality would wish each other "be well" instead of "good bye". This excessive congeniality made them sound exceptionally naive.
A more common expression is, "Take care!", even if the person is not about to do anything dangerous.
I started saying this a few years ago. I still use "goodbye" and other idioms, but when I say "be well" I mean something more emotional, deeper. It's my way of saying, "For however long passes between now and when we next see each other I hope you have a good life. Have a joyous life. A prosperous life. A healthy life. The life you most desire. And when we see each other again let us rejoice."
Chris Cuomo, CNN, uses it nightly on his show. I personally like it and feel like it connects better with the recipient, like you sincerely want and hope the best for that person until you meet again.
I, too, just started using this in person as a form of goodbye and in writing as a salutation. Desiring all good things for all people. It is certainly most appropriate in our current unsettled, global paradigm regardless of the audience. It is synonymous with thrive. Be well!
This question is likely a matter of opinion. "Be well" is certainly not a typical departure phrase.
I have sometimes heard this phrase used by people who strive to be alternative (a theme in my community), and use language that is intentionally different from many other people's.
I also just recently saw this phrase used in email and other electronic message signoffs to a friend who has been extremely ill. In this case the phrase could be a wish that the person becomes well, or could be an attempt to avoid saying "goodbye" (again, this is a matter of opinion), which could sound, well, final, or "see you later," when there is a good chance that will not happen.
It is often used to also end an email and let the other person know you are ceasing further dialogue and don't expect a reply.
I have been using Be Well for more then 8 maybe even 9 years or more. I don't do goodbye anymore.
I started doing it because good is way to light or dark in the use of words good also does not say much on parting. Be Well handles a lot better, it leaves a lot for the one who hears it to place it on a scale themselves. Take care sounds like their is risk at every turn. Where I would use Be well and safe travels, I am drawing perception to the idea of more awareness when driving or travelling. Or safe journey, also works I may even use have a happy morrow. As in wishing their next day well, but I also tend to let people know when I am leaving to do something else or going to my room so they know they have more privacy when we have shared company.
Be well is informal synonymous of good bye, just like cya, peace, later and so..