League of Legends (LoL) Question: Question about Nunu jungler

Nunu & Willump is a top tier jungler and far from useless.

To answer your question: Nunu & Willump works the best when you go to the enemy jungle and deny xp/gold by counter-jungling the opponents jungle. Counter-jungling requires lots of vision in the enemy jungle so it's more cost efficient to just get Sightstone than keep buying tons of wards.

You need wards to know where the enemy jungler is and if anyone from the enemy team is coming to help the opposing jungler. It's risky to go to the enemy jungle without knowing where the enmies are and that's why Sightstone is needed to grant you vision so you know where everyone is moving.

It's useful to cover for objectives too as you can pretty much solo dragon on your own if you ward up for it.

i think nunu is far from useless being able to solo dragon as soon as he gets cinder hulk and taking relatively low damage doing it plus he counter jungles very well

It's because Nunu is Quote "Useless" and his job is to basically make an enemy as uselesss as he is. His Q does nothing besides sustain in the jungle, building damage is not smart, he has amazing sustain, more wards = wins. You are basically a support put into the jungle, the only way that it works is because of his q. You don't need to tank a lot since after you use your ult, Blood boil and iceblast you are just a useless nunu, you have no more peel or damage so there is no reason for you to tank or even live any longer. So since sightstone isn't the best tank item, it's perfect. Also i've learned that getting it on other tank junglers is fine because of the 25% health increase on Cinderhulk, I get it sometimes when playing sejuani.