Could have a use-case for this..
I use Sophos UTM as my home firewall (used to be Astaro Linux then it got borged by Sophos - fortunately they didn't hack it around much and honoured existing home, free licenses..).
The issue is that they don't support UEFI booting. My old firewall is an elderly HP Microserver - Intel Celeron processor... Which was OK in the old DSL/VDSL days - or even the FTTC dats since it was capable enough to keep up with the bandwidth available. Then I got FTTP (900Mb) and it's struggling..
So I bought myself a refurbished Dell Poweredge T40 - nice little server with many multiples of CPU uplift over the old HP.
I soon discovered it wasn't going to work - Sophos UTM will not boot from UEFI and the T40 *only* allows booting from UEFI (or so it seems - I couldn't find a BIOS boot made in the usual places in the BIOS).
But I could stick in a small USB stick, tell the Dell to boot from that and have it chain-boot from /dev/hda thus booting into Sophos UTM.