Addresses an issue that could cause Messages conversations to temporarily be listed out of order.
The macOS High Sierra 10.13.3 update improves the security, stability, and reliability of your Mac. To enable Messages in iCloud, go to Preferences in Messages, click Accounts, then select “Enable Messages in iCloud”. This update adds support for Messages in iCloud, which lets you store messages with their attachments in iCloud and free up space on your Mac. The macOS High Sierra 10.13.5 update improves the stability, performance, and security of your Mac and is recommended for all users.
Better graphics and VR supported have also been included along with backwards compatibility so you install the new OS in machine even from late 2009. There's a new file system, AFS, for better security, reliability and speed in file transfers. MacOS High Sierra is packed with new features and refinements.