You don't have to use the lube over the bullet and a wad too, or if you use a wad, such as a Wonder Wad of the appropriate diameter, you can omit the grease on top of the ball.

The purpose of either is to lube the round, or course, but mainly to prevent flashover or chain-firing where more than one chamber goes off simulataneously!

Personally, I prefer to put a Wonder Wad under the ball. It is a lot faster and much cleaner/neater than fooling around trying to squirt a gob of grease into each chamber afterseating the ball. If you put a wad into each chamber mouth after the powder charge, it will prevent any powder spillage from happening before the balls are seated.