Below you will see a checkbox for "Allow booking request" with an Airbnb logo next to it.
If you check this box, guests will have the option to submit booking requests inside of your booking lead time window.
In this example, if you check the box and have your booking lead time set to 48, no one can instant book within the booking lead time on Airbnb, but they can still send you a booking request.
This can offer you as a host more flexibility in accepting bookings. Maybe you are very cautious of allowing instant bookings within 48 hours of the arrival date due to logistics of cleaning the home and ensuring it is guest ready. You can still keep that control of not allowing those instant bookings, while enabling guests to submit booking requests to you in case you do think you can ready home in time.