Britney -singer, dancer, lip syncher?

Though I'm not a big fan of her music, I am glad to see Miss Spears appears have stopped shaving her head and waving her bare coochie around town. It's always kinda sad to see a mother of two small chidren go completely off the rails.
But while it's good that she is on the mend and all that, can anyone explain to me the point of her-or anyone else- going on television and lip synching? I mean really? Why bother? If you can sing why not sing? Especially on a show about people trying to make it singing.
By the way I don't watch X Factor but it was on in the gym yesterday and my battery had died in the pod. This or Ne-yo were my options. And you try running to Ne-Yo. Actually try running to 'womanizer' either, not pretty.