Even on traditional BIOS systems, you can do tricky things like use isohybrid to generate an iso that can be either burned to optical media, or directly dd'd to

Even on traditional BIOS systems, you can do tricky things like use isohybrid to generate an iso that can be either burned to optical media, or directly dd'd to a thumb drive and booted (using syslinux). Another approach (my personal one) is to use a combination of grub/memdisk on a thumb drive to provide a list of bootable isos.