So, according to Chapter 02 of the SystemD LFS documentation, it looks like there is an LFS environment variable and user that will need to be set for various later instructions that will make any product resulting from use of those instructions a derivative of LFS.
While I’m still on iteration 0, I want to mark these as found so that during Iteration 2 I will have a clear path for an independent Linux build.
After reading a little further, it looks like they’re going to bootstrap builds from a parent system and use the $LFS variable as a placeholder for the mountpoint of a dedicated filesystem that is storage for the resulting binary objects of any builds that are done. So this is really just a convenience factor. The reason for having a dedicated user is still unclear.