Pre-orders let you fund a production run with customer money and set quantities from real demand, including real size data. They are common for first drops, band merch tied to a release, limited collaborations and anything with custom fabric or a long lead time.
The trade-off is waiting. Customers need a clear ship window on the product page and at checkout, and updates if it moves. Production delays land on you directly, so the date you promise should cover production, finishing and shipping with a buffer. Mixing pre-order and in-stock items in one cart also needs a plan: ship together or split.
Check your store platform's pre-order tools and payment capture options, and your payment processor's rules on charging before shipping. See pre-orders vs stock drops and Shopify pre-orders.