You can now send calendar files in Android Messages app. It's not that useful feature but in case you ever want to send calendar files in the messages app so you can use this feature.
I don't know what through made developers to add this feature but it's good to get new features and updates.
Latest Messages app version 3.9.039 includes this feature which you can install in any Android 4+ devices. Below we have shared the official change-log of this update.
How to use Calendar sharing feature:
You need to use a file manager app to share the desired calendar file in the Android Message app. Once you select the file & click on the share button you will see the Messages app icon there.
If you don't want to wait for this feature to come for your phone in Play Store, so feel free to grab the latest version from below APKMirror link.
Or Keep updated your message app from Play Store.