Many have too few SATA ports in their rigs to be able to install multiple hard disks. Hard disks do not use a lot of power so there is little stress to installing a full cage of high capacity disks.
The JMICRON JMB575 supports SATA, SATA II and SATA III speeds. The older JMB321 only supports SATA and SATA II speeds. The JMB575 based cards have a SATA power connector and it can be cascaded to support 15 drives.
The JMICRON JMB575 is supported by Windows 2000 and above. Port multipliers are full bandwidth but SATA III is limited to 600 MB/s. SATA port multipliers are best for their archival capability. A low cost µATX motherboard with 4 SATA ports can control a chassis with 60 hard disks in an archival server using cascaded SATA port multipliers.
The performance of the low cost 5-port units is surprisingly fast. While most uses these for hard disks, they are fast enough for SSD drives as well. The port multiplier is not a RAID device, each disk is its own device id and drive letter.
The standoffs make it possible to mount the logic board to the motherboard tray securely. Fortunately the SATA ports are planar so the narrow cable area is easily managed.
The standoffs also allow several SATA port multipliers to be mounted in a file server. This makes it easier to route cables to the various disks.
The USB 2.0 hubs are not insulated. The double sided tape also acts as an insulator to protect the hardware. The way the USB 2.0 headers are presented make it more challenging to place securely.
Unfortunately the internal USB 2.0 hubs do not have a power connector so they are unsuited for BCC 1.2 charging or supporting a USB hard disk. By comparison the SATA port multiplier has a SATA power connector to provide the logic with adequate power. Berg connectors are low cost and small which they are seen on some devices.
Front panel boxes for 2½” disks are overpriced. There is not much more than some metal parts and cheap connectors. The SATA multiplier chip is not very large and it could be easily integrated into a unit like the ICY DOCK box.
SATA cables are very low cost making the SATA port multiplier a low cost way to install vast amounts of storage at low cost. Backblaze uses several of these port multipliers to be able to install 45 to 60 hard disks into a chassis.
Larger EATA chassis such as the old Cooler Master HAF 932 or the Corsair Obsidian 750D have several internal disk bays. The SATA port multiplier card solves the problem of insufficient motherboard resources.
SATA power cables are available for supporting the same 5 SATA ports as provided by the SATA port multiplier. This makes integration easy.
The SATA-IO standard includes NCQ and Port Multipliers. Port Multipliers are best with AHCI mode and NCQ hard disks. Frame Information Structure (FIS) based switching offers high performance storage connections to multiple drives simultaneously. The host issues and completes commands to drives at any time. The port multiplier will direct data to any drive ready for I/O. An arbitration algorithm ensures a balanced data flow.
NO MOTHERBOARD SUPPORT
To my disgust neither Intel or AMD motherboards support the port multiplier. The lack of support means they are not compliant with the standard.
Marvell cards work fine with the port multiplier. So do the Silicon Image cards. Most likely server cards have general support.
Modern port multiplier cards are a low cost way to add more storage. This makes sense with larger game libraries.