Because most people are highly suggestible to subtle energies due to a lack of awareness, and with an unwinding of your astral body’s energy knots, you open yourself up to for a lot of things “out there”.
When the ADC is accompanied by an energy field that immediately acts on the astral aspect you’re dealing with, it’s a bit safer.
I say mandatory simply because, why risk it? Even if the risk of hi-jacking is 1%, knowing that you could have a trojan horse scenario on your hands, reprogramming your entire being, why not just make the risk 0 by using a shield?