Update I have 1 shotted Yone with E and Q and Ashe with only Q but I had like over 900 stacks and Infinity edge in my build.

You will get mana lifesteal and you did get dmg from runes and cd.
I like nasus because my games can be long and you just stack, now you can 1 shot with my build.
Watch carnarius videos.
I like to turn auto attack off in begin so it is easier to lasthit and then turn it on.
I got 0,7 second cooldown on Q with ult and killed adc with 2 Q.
Nasus is good for beginners and i like nasus because i want to do some dmg and buil some hp. Nasus passive is to good i think because it gives you hp when you basic attack and Q so lategame you can get your hp back in just 1 wave or jungle camps. You can also take dragons solo and I do it most because my jungle and adc dont do it. help jungle with rift herrald. dont take tp, because yes it is good you can get back to lane and gank etc but you wont get them you are slow. Also in lategame you will get kills so you want to chase them and for every kill it lasts longer and you get bonus movement speed from deaths dance.
I take trinity force because i dont play against many tanks and i want to know how mych dmg my items does. So for example divinde surender does 10% hp of enemy but if enemy has 2000 hp it does 200 dmg same as trinity.
divine gives 50% of dmg dealt from item as lifesteal. so it can be small hp back. and armour pene if you have items.
Trinity i love because it gives in new season all things nasus need. Nasus needs cooldown it gives 20 ability hase instead of 10. and movement speed. And also attack speed. It is good because i move faster and can land my Q faster too even if iit is auto reset. Bonus if you have black cleaver you can pene faster with your autos.
I take death dance because it gives armour and you dont get 1 shot, it helps me dive in under towers too with movement speed when i get kills so i can run away with my 100 hp. it gives cooldwon and ad so if enemy is full ad i can go this item first too.
I take dd because it gives ability haste armour pene dmg and kills i get stealth. So it will get easier to kill and run out or kill and go for next. and now you think no you will get revealed from death dance passive but no it resets so no true dmg wile im invisible.