What had the two men decided to do to make the ladies happy?

The two men are decided to be christened, like this, they will change their real names (Jack and Algernon, in that moment) to Ernest, their wifes favorite name for an "earnest" man like them. But, finally, they aren't christened by Chasuble, because, Lady Bracknell comes back and Jack doesn't thing that a christening would be the practical value for either of them. True? Someone can explain what means " the practical value"?