The fields stored in the log have changed across Sierra and High Sierra. Analyse them on the wrong system, and you could lose content without being aware of it.
Signposts
Support for the unified log’s new features in both High Sierra and Mojave, including Signposts and performance analysis. Now, and free.
Changes include an additional output text format, display log since the last boot, and support for Mojave’s Signposts is already present and being used by Apple.
After 2 years, developers should be able to use the unified log for performance analysis, thanks to extensions and Xcode’s Instruments. Sysadmins and users remain neglected, though.
The Eclectic Light Company 