Yeah you don't know until you actually have someone choking you out exactly how far you can go. I've never been choked out but I've tapped and stood up to fall over again on some other lightheaded trip. I don't think it's necessary but with anything in life... If you don't like it, tap. Usually it's not depriving the brain of oxygen, it's usually you depriving it of blood that shuts it off.
This has a dramatically less chance of causing damage than if you lose oxygen to your brain.
Remember that there are people with low blood pressure that faint cause of it.
It's not something the body is totally opposed to but that's why they made tapping.