What reason is there to actually erase your internal hard disk?
Just to force the Mac to boot it's OS from an externally connected drive?
You can set the startup disk, so I'm not sure that would be the reason.
Maybe the Mac puts the external drive to sleep then, and it stops producing
any heat inside that small case.
I read that, first, from the point of view that if it all went to hell I could get
another Mac mini fairly cheaply, but it occurred to me that if only the internal
HDD failed, I don't have anything to copy Mac OS from, so I went ahead and
got a SATA adapter, and now have that bootable clone drive
Still don't seey why deleting the internal one is a good idea.
Looks like Macs with USB 2.0 only boot Windows 7/8 from the internal drive.