I looked around a little, can't seem to find the following...
Is there (where is it?) a Thank You email template? As in thanking them for staying, mentioning our website, nice request for review, maybe chance to book or refer others in the future (with a discount), etc?
You can customize an email template (Settings > Email Templates > Create Custom Booking Template) to say anything you want and then use a trigger to send it [x] days after departure.
Here's an example template: