I have several SLES machines in production and never used this. Here's a good overview: https://firmware.intel.com/sites/default/files/resources/A_Tour_beyond_BIOS_Implementing_APEI_with_UEFI_White_Paper.pdf
Hardware Error Source Table (HEST) The HEST table enables host
firmware to declare all errors that platform component can generate
and error signaling for those. The host firmware shall create Error
source entries in HEST for each component (such as, processor, PCIe
device, PCIe bridge, etc) and each type of error with corresponding
error notification mechanism (singling) to OS. These error entries
include x86 architectural errors, industry standard errors and generic
hardware error source for platform errors. The x86 architectural
errors, MCE and CMC, and standard errors PCIe AER, MSI and PCI INTx
can be handled by OS natively. The generic hardware error source can
be used for all firmware 1st errors and platform errors (such as
memory, board logic) that do not have OS native signaling, so they
have to use platform signaling SCI or NMI.
I guess if you really want to monitor all the hardware errors this might be useful.