Running rescue disks without removable media?

I think someone once told me about just “installing” a rescue disk instead of formatting it onto a USB or CD and running it on BIOS. Is that even possible? Would it even run pre-boot? Would it even be as safe as booting from removable media? I can link the message, but only if people need to see it for proof because maybe I misunderstood what they said and I don’t want them to look bad.

submitted by /u/GuyswabThreepwood
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