Tax-advantaged saving for college expenses.
529 accounts function similarly to Roth IRAs. You pay taxes on your inputs to them now, but you don’t have to pay taxes on growth at the time of withdrawal. The difference between 529s and Roth IRAs is that the target withdrawal scenario is college, not retirement.
In both types of accounts, you can can take withdrawals of any contributions at any point without paying penalties. In order to also withdrawal the growth portion of the balance you must meet the requirements.