Comment 2 for bug 1909168

TFTP was just an example. HTTP would be fine too. The point was just to allow the installer to request preseed information early in the process via DHCP.
This was for a poor-man's partially automated boot setup (not full PXE).
Think of using a USB drive (or .iso for a VM) to boot from the "standard installer", but then preseed most/all of the the usual installer questions questions that don't vary across versions or that may be specific to that network location (e.g. apt proxy info).
Yes, probably a limited use case, but still a nice time saver.
In the past this was easier than rerolling an installer image to have the files embedded.
Now I guess one can prep a separate USB drive with an appropriate label, which works well enough.