lets see something more dangerous than promethean vision
you see the persons skeleton their muscles and their cardio vascular system.
from that one target you can see BPM of their heart their muscle contractions so you can kinda predict how they will move but it takes practice.
it does little to make him more powerful it however makes him more lethal and tough to hit.

the drawback is its extreme tunnel vision
he cant properly focus on other important targets..one at a time
inpractice he can track two then three...perfectly
he needs a direct line of sight on the target to initiate it but cant just pick a person out when he cant see them