SB-600 and the D300

Hi all

Just about to take possession of a D300. I’m coming from a D50 and all I’ve ever used is the pop up flash. Was wondering whether it would make a significant difference to my flash photography if I picked up a used SB600? For indoor shots of my very active family, etc, would the SB600 be more useful to me than the pop up? What would be the benefits of getting the SB600 in the long run over the pop up?

Would appreciate feedback. Many thanks.