Hello,
these settings define if to use the working time for lead-in and lead-out times.

For example, you you have a 30 minutes Lead-In time configured for a service, and your working hours start at 10:00.

So if this "Use Before/After Working Hours Time For Free Time Before Appointment" is On, the client will be able to schedule an appointment at 10:30 only, the 10:00 - 10:30 period will be used for Lead-In

If this setting is Off the client will be able to schedule an appointment at 10:00, the Lead-in will be in the non working time before that (9:30-10:00) - it will be the business owner task to come earlier and get prepared for the client.