Some Theosophists think its unhealthy if you do a lot of it. In their minds, your 'astral' body is an essential part of your physical body, and if you decouple them too much, there are mental and physical health implications.

My own view, tentatively, is that there is no 'astral body', that its a mental map of your capacity to feel sensation within your physical body. So when you astral project, you're not actually leaving your body, you're just screwing with your perceptions. You do need that map to operate your physical body though, so I suppose if you went overboard with confusing it there would be mental health implications. I'm also 100% sure that this view doesn't capture the whole essence of astral projection though, so I can't rule out other risks. It seems to me that the best thing is not to make any assumptions. If it seems unhealthy to you, don't do it, if it seems healthy, do it, and don't let other people's fears or careless arrogance trump your own instincts and objectivity.

In my experience its definitely not 100% bull. Maybe its 80% bull, if one can pretend to put percentages on such things, but the other 20% is objectively real.

I don't think its possible or desirable to go off in the astral body and not come back, because in any plausible interpretation of what the astral body is, it has a dependence on the physical body. If it was possible to astrally project permanently, which I doubt, you'd just be dead, pretty much by definition.