Pro - carries heavy loads better.
Con - makes pack less flexible, worse for climbing. And heavier.
IMHO, a daypack sized pack only needs a framesheet if you're carrying skis and boots on it. Try it sans sheet, if you don't mind, you're good to go. If it bugs you, you can cut a new framesheet out of the lid of a plastic walmart storage bin.
And what the hell is a cubic liter?