Contributing to 401(k) and Roth 401(k)?

My employer offers a 401(k) and a Roth 401(k). They match up to 6%. I am getting my full match. Currently contributing 10% to my 401(k) and 2% to the Roth 401(k). I am over 50 so contributing Catch-up to both. I can’t recall the reasoning that led to me contribute to both.

Is there a good reason why I should contribute to both?