Depends on the distance. Last year I got my deer with a really hot load of 3 1/2'' 00 buckshot from 35-40yards. It dropped him on the spot possibly because a pellet hit the spine, but he was still kicking around and I didn't want to see him suffer for more than he had to. Since I didn't want to scatter another 15 pellets at his back or side from that distance and possibly damage and waste a lot of meat, I hurried down my stand and ran up and gave a quick shot from 5 yards to the heart/lungs. It was pretty fast after that.
Typically though, just aim for a follow up shot either in the vitals or head that isn't going to damage too much meat but is going to put them down as quick as possible.