Most Helpful Guy
You can only tell if it's exaggerated on purpose and used as an effect. If it's used for slight pitch correction, which is what it was designed to do, you'll never know, at least not by listening.
As with most effects, it's overdone and quickly becomes tedious to the listener. The first big hit to use it as an effect was Cher's 1998 hit "Believe":
I've used it on my own recordings because sometimes you have a magical, inspired take with a pitch problem that's better than all your other takes that are perfectly on pitch. You can also use it to thicken a vocal by leaving the original and the pitch corrected version together in the mix. It creates a chorus effect. To do this, the original has to be basically on pitch. Still, humans don't ever reproduce frequencies perfectly, which allows you to create the effect. (There are amazing singers who can come close.)1