Exactly. Or if the power supply is broken... or the CPU, or the RAM, or anything that requires the iMac sent off to servicing.
Also, I'd need another Mac to access the data, whereas with a USB-SATA enclosure I could use anything that runs Linux (as there are HFS+ drivers for it). For the new breed of cr.p Apple has forced upon us I'd need a Mac AND a Thunderbolt Cable AND the luck that the source system is still bootable.
If you're using HFS+ then you can put the system in target disk mode and access it from any machine with an HFS+ driver. Not sure if there's APFS support in linux yet.
How to put a machine that does not boot (any combo of fried CPU/motherboard/RAM/PSU) into target disk mode? Or, when the machine boots but you don't have a Thunderbolt link cable?
That's the core question. Apple needlessly deviates from any standard.
Also, I'd need another Mac to access the data, whereas with a USB-SATA enclosure I could use anything that runs Linux (as there are HFS+ drivers for it). For the new breed of cr.p Apple has forced upon us I'd need a Mac AND a Thunderbolt Cable AND the luck that the source system is still bootable.