Of course in the last twenty-five years I don't think I've ever really used a system set up like that. But it does seem nice to at least be able to do so.
The first PC I built had 7 disk drives in a tower case, four distinct hard drives. Yes it was crazy. But the largest of these by far was 540 MB. It made sense to keep the boot stuff on its own hard drive.
Linux has `boot`, of course, but `boot` should never appear in $PATH. I think.