The Beatles famously never played any live performances of anything from Sgt. Pepper since it wasn't possible to reproduce the complex, layered sounds they created for that album.
Nowadays, of course, anything is possible. But it's still surprising that this is the first time that Being for the Benefit of Mr. Kite! has been performed live by a Beatle. Paul McCartney is currently on tour in Brazil and will soon be bringing the same set-list to the US.
It's great that McCartney chose this song for a live performance. It seems to go down especially well in Brazil (I have received many wonderful comments from people in that part of the world about the Mr. Kite poster). It's also fantastic to hear the crowd going crazy for this song and singing along with the words.