In the build it will let you choose to be defensive or offensive being offensive can let you kill more faster but die chance be high defensive also being offensive can let you have a higher chance for your e and ult do much more damage then base damage.

The abilities upgraded in that maxing you e first can increase the damage it does and reduce the cool down it has and for q it will just increase damage and reduce the cool down while for w being last because its just for melee it won't help in chasing down your opponents it will help against tanks but won't be good for chasing which is very important because then you can tower dive and not take that much damage if you e CORRECTLY because e can help you in a lot of ways such as dodging ult like cait ult or fizz ult so this is why you max w last and e first so e makes you survive much more but still in chapter one defensive is still a good choice because it will lower the chance of you dying.

The Masteries Ability power because it will make all his abilities more powerful so does the runes magic is very important going attack damage won't be good do to it won't empower most of your abilities.

(this has not been used for ranked yet)