Rotors running
I think there are many factors to consider and what may be deemed safe in one type is not safe in another.
Other factors to consider is weather. Would you leave a helo running in high winds with gusts?
Unfortunately there are a number of pruners that know of NB who died after being struck by his helo blades.
Not something I will be doing because if something goes wrong it's never going to be pretty and likely to result in serious injury or fatalities.