Quick answer
Book Time Off emails you automatically. You get a confirmation when you submit, and the decision when your leave is approved or declined. Approvers get a request email with one-click Approve and Decline links.
When you submit a request
You get an email confirming it is submitted and awaiting approval. Your approver gets an email with the details and one-click Approve and Decline links.
When it is approved
You get an email letting you know your leave has been approved, and the days come off your allowance.
When it is declined
You get an email letting you know it was declined, so nothing is left unanswered. Speak to your manager if you have questions.
These are automatic
The submit, approve and decline emails are sent automatically and are not individually switched off. There are no reminder emails.
Slack and Teams carry the same updates
If your company has connected Slack or Microsoft Teams, requests and decisions arrive there as direct messages too, with the same one-click Approve and Decline buttons for approvers. Google Chat can post the daily who's-off digest and let people book leave, with the approval decision sent to the approver by email. See Use Book Time Off in Slack and Use Book Time Off in Google Chat.