Remember your body isn't as fast as you can track. Can perceive to react but your body will still only move at the speed following the speed chart laid out in the guides section.Perception wise, EMS can essentially bring time down to a crawl, as long as my Bio has the necessary tracking level, you can essentially see the whole world in hyper slow motion, able to see even the most minute details of a technique. To the opponent, the jutsu may hit in a second, but to the EMS, you would see the jutsu take a full minute to get to you, as an example. You're also able to spot the smallest inconsistency in jutsu and genjutsu, allowing you to spot essentially everything.
Tracking Wise, i explained most of it above, but you can also predict how your opponent will follow through with their strike, watching their muscles and chakra control, pinpointing where they will finish their strike, or even how they will begin it, in super slow motion.
Predicting natures has always been the thing Sharingan i never fully understood. From my knowledge, Sharingan perceives natures not as they are, but how the chakra behaves, so, Lightning will be fast moving, water will be fluid, fire aggressive, ect ect, with the EMS, due to the huge perception and tracking boost, watching my opponents chakra flare up also comes down to a crawl, allowing me to essentially watch the technique grow inside them, from raw chakra, into whatever nature it will turn into, i believe. But as said, user has to have seen it or know it to predict the actual jutsu, but i can predict what nature a jutsu will be and counter properly.
Genjutsu, EMS can cast any genjutsu just by seeing the opponent, and uses the Sharingan as a medium for handseals, essentially glaring your chakra into them, locking them in genjutsu. EMS is also able to see through Any ranked Visual Genjutsu, being the pinnacle before Rinnegan which just makes you completely unable to be put into a visual genjutsu in the first place.
You can see the build of chakra, and percieve it as it's released, seeing it in slow motion. The way you will predict the nature will be based on seeing the jutsu before (cannon or having fought the opponent before in the nw), the handseals used (which is a pain with current specialities) and so on. You will see it on release, but chakra is just chakra in their body until it's released. Handseals were invented to help people form this chakra, forming ninshu. The arc with hogoromo's son's is a great watch for explaining how chakra and jutsu work on a base level and with that it might help with how you read jutsu that are being used. The most common thing we have seen is through kakashi, he can see a jutsu, the way the chakra is built up and the handseals used to then form it himself, using it to be the copy ninja. Like he was the water dragon once, read all the handseals, memorised them, saw the build up of chakra, the shape, how it was released and the nature. Through this he was able to perceive Zabuza doing it, and do it at the same time. In perceiving and getting used to how zabuza fought, he took it one step ahead and made it seem like zabuza was copying him. Watch that fight again for clarification on reading jutsu.
To be fair, you can't cast "any" genjutsu, if a gen needed a flash or a sound to induce it, you wouldn't be able to perform it in this way, by looking at them, just to be clear.
"While granting the user the ability to perceive the world with increadible insight, it also grants the user the ability to see through S-Rank visual illusions "
You can see through S rank visual illusions. This would not include F ranks or genjutsu boosted above S rank. Only the rinnegan will be immune to visual genjutsu. I don't believe you will be able to see through yin gen though, i'm not 100% sure on this one so i will check.
Any questions?
If not tell me all you know about amaterasu.