I discovered two things after upgrading to Sierra: 1) Huge space savings! On my 12" Macbook it saved 30GB and on my wife's 15" Macbook Pro 69GB! This is without storing anything in cloud or doing any kind of optimization. 2) Safari is flying and both Macs are noticeably faster.
Reading all the negative comments here, I was rather sceptical about this upgrade but seeing the results on two machines, I changed my mind.