I find this discussion ever so intriguing but utterly incomprehensible. [...] So:
• Why [....] ?
In a nutshell (and not exhaustive):
- (Bootable) clones are independent and complete backups identical to the original that can be used when the regular boot drive malfunctions. Clones are an option to preserve important data and (when bootable) to limit downtime to that of a restart. For obvious reasons, having such clones located on separate hardware increases their usefulness.
- An enclosure is a box housing (currently mostly) sATA-interfaced devices like HDs, optical drives etc., fitted with a power supply and an interface board for ports like USB, FW, Thunderbolt etc. Usually you purchase enclosure plus enclosed mechanism together as a single unit. You might also use an enclosure to house an internal drive you replaced with a larger one. As any hardware item, enclosures may harbor problems separate from the items they enclose.
- Connections/ports (USB, FW, Thunderbolt, cables etc.) matter because they are independent and independently fallible, in addition to having different specs and foibles. Physically, connection issues can be anywhere in the entire chain from computer (buses, ports, controlling hardware etc.) via connecting cables to peripheral hardware (enclosure, sATA device and associated controller boards).
Standard troubleshooting techniques may localize problems to any of the items discussed here, as is the case with the enclosure in this thread.
