This supplemental update includes improvements to the the stability, reliability and security of your Mac, and is recommended for all macOS High Sierra users. This update:

• Improves installer robustness
• Fixes a cursor graphic bug when using Adobe InDesign
• Resolves an issue where email messages couldn’t be deleted from Yahoo accounts in Mail

For more information on the security content of Apple software updates, please visit this website: https://support.apple.com/en-us/HT201222