I am reasonably certain that the partition type GUID B8CB5058-C187-4719-BAF0-379CA2D4C97E is used for ExpressCache partitions. Since Wikipedia articles must not contain original research, and I was unable to find a source to corroborate (or refute) this finding, I am documenting it here.

My Findings

While working on a Lenovo ThinkPad Twist S230u Laptop, I noticed that it has a 24GB mSATA drive (Samsung MZMPA024) with the following partitions:

Disk /dev/sdb: 22.4 GiB, 24015495168 bytes, 46905264 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt

Device        Start      End  Sectors  Size Type
/dev/sdb1      2048 32223231 32221184 15.4G unknown
/dev/sdb2  32223232 46903295 14680064    7G Intel Fast Flash

The sfdisk dump contained the following information:

label: gpt
device: /dev/sdb
unit: sectors
first-lba: 34
last-lba: 46905230

/dev/sdb1 : start=        2048, size=    32221184, type=B8CB5058-C187-4719-BAF0-379CA2D4C97E, uuid=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX, name="Basic data partition", attrs="RequiredPartition GUID:63"
/dev/sdb2 : start=    32223232, size=    14680064, type=D3BFE2DE-3DAF-11DF-BA40-E3A556D89593, uuid=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX, name="Basic data partition", attrs="RequiredPartition GUID:63"

The 7GB second partition with type D3BFE2DE-3DAF-11DF-BA40-E3A556D89593 appears to be for Intel® Rapid Start Technology. The first partition type is not documented anywhere that I can find.

The machine has the Lenovo ExpressCache Software for Windows installed. Running eccmd -info to check the status (per Lenovo ExpressCache mSATA troubleshooting) yields:

ExpressCache Command Version
Copyright© 2010-2014 Condusiv Technologies.
Date Time: 10/6/2018 10:35:45:67 (LENOVO-TWIST #4)

EC Cache Info

Mounted                   : Yes
Partition Size            : 15.36 GB
Reserved Size             : 3.00 MB
Volume Size               : 15.36 GB
Total Used Size           : 6.70 GB
Total Free Space          : 8.67 GB
Used Data Size            : 6.63 GB
Used Data Size on Disk    : 6.69 GB

Tiered Cache Stats
Memory in use             : 0 Bytes
Blocks in use             : 0
Read Percent              : 5.96%

Cache Stats
Cache Volume Drive Number : 1
Total Read Count          : 64828
Total Read Size           : 3.52 GB
Total Cache Read Count    : 22994
Total Cache Read Size     : 2.01 GB
Total Write Count         : 9361
Total Write Size          : 194.17 MB
Total Cache Write Count   : 6256
Total Cache Write Size    : 96.51 MB

Cache Read Percent        : 57.12%
Cache Write Percent       : 49.70%

Which describes an active ExpressCache on a 15.36 GB partition. Since there are no other partitions of similar size in the system, and the Lenovo documentation mentions mSATA drives specifically, it seems reasonable to conclude that this is the mystery partition.

Talk:GUID Partition Table/Archive 1 mentions this GUID “is used by SanDisk express cache”. It also links to a SuperUser answer which identifies the type as Intel Rapid Response (with a comment claiming Smart Response). Since the drive also contains a Rapid Start partition (discussed above), I suspect that may be the cause of the confusion.