I would say always use a hood. Using one saved my 24-70 from a fall!
One thing about the 24-70 hood is the size of it! I can see how that would work, but ... don't be dropping your lenses!![]()
I know I was glad I had mine on when I was shooting in lashing rain yesterday, kept drops off the glass - but not much else. It's useful when it's real sunny too , to prevent flare. But why is that hood so bloody huge??
Someone mentioned street photography - the 24-70 is a savage lens for that purpose, but with the hood on you stand out like a huge throbbing sore thumb!