Booking links are used for simple, automated scheduling. Yottled looks at your Google calendar to find out when you're available so a client can find a time that works for them. When they schedule with you, they pay your rate, both you and your client get an email confirmation, a calendar invite, and video information to connect.
The Public setting enables anyone to book the appointment. It appears on your Yottled site and anyone can book it.
The hidden setting enables only people that have the link to the specific appointments to be able to book. As the host, you'll be able to see the appointment on your Yottled Page but contacts will not be able to see it. In order for a person to find the unlisted booking link, you must send them the link.