Email trigger - Difference between Booking has arrived and Blocked off time has started

I'm starting to set up my first automated emails. Check in instructions, thank you for staying, etc.

My first question is:

What is the difference between "Booking has arrived" and "Blocked Off time has started"?

Is there a good forum thread or blog post that discusses setting up these emails?

Thanks!

booking means booking for actual people, on the day of check in. ex: booking May 27 - May 30, booking has arrived would be May 27. Blocked off time is just that - calendar block (like you block for maintenance, there is no actual booking), and blocked off time starts . if you blocked off may 27 - may 30, the blocked off time started will be May 27.