What are the differences between pre-tax deferral and Roth 401(k) contributions, and how do they impact retirement savings?

Pre-tax deferral contributions are made with money that has not been taxed yet, reducing taxable income now but requiring taxes to be paid upon withdrawal in retirement. Roth 401(k) contributions are made with after-tax money, allowing tax-free withdrawals in retirement. The choice between the two impacts the amount of taxes paid now versus in retirement, affecting overall retirement savings.