My build of LFS is 64-bit but is not multilib, meaning it does not support building or running 32-bit binaries.
My impression is that the biggest uses of a 32-bit compatible environment within 64-bit GNU/Linux is WINE (an environment for running some 32-bit Windows applications) and some games.
There also are some closed-source applications, like an AAC encoder that used to be popular before FFmpeg caught up, that were (or are) only available as 32-bit binaries.
Multilib is a low priority for me but when I do it, what I hope to do
is install the 32-bit environment within /opt/compat-32 as the install
prefix rather than /usr which then forces the use of /{,usr/}lib64
for the 64-bit libraries.
Another possibility is to use /{,usr/}lib32 for 32-bit libraries,
but I would rather just put the 32-bit environment within /opt/compat-32
and not have to use bit-specific library directories.
I have no plans to support a 32-bit bit build of YJL. 64-bit systems have been the standard for about two decades now.