This statistic shows kernel memory which is allocated, and can be broken down by kernel cache (kmem cache).
An understanding of operating system internals is required to understand this statistic.
Rarely. If the dashboard were to show kernel memory as a large consumer of available DRAM (in the Usage: Memory section), then this may be used when troubleshooting the cause. Also see Memory: Kernel memory in use and Memory: Kernel memory lost to fragmentation.