Most businesses will automatically play a recording if you try to call their office when they are closed. An after hours announcement is a professional way to notify callers of important details, rather than making them wait for the call to failover to a voicemail box or other destination.
18. "Hi, you've reached [your name]. I'm away from [date] to [date]. If you need help with [X] before then, please contact [name] at [phone number]. Everyone else, please leave your name and number and I'll return your call when I return. Thanks and have a great day."

My consultants sometimes do. The information tends to be "please call us back", but on the other hand said callback request tends to include a direct line that's not trivially publicly findable, so.
People around us can need help at any time of the day. Many a time friends, family, boss, colleagues, relatives, and acquaintances need to inform us of something important at odd hours. Some may know when to call you and some of them won’t. In cases where you are not accessible, leaving a simple voicemail on your phone can ease their worry.