You assume everyone has root.

On a system I don't administer, I can compile and install software in my home directory (or shared directories that I have write access) by using:

./configure --PREFIX=/home/myuser/software/

make # to compile

make install #without sudo, to install to ~/software/bin

So when you say "only in (B)LFS", you're overlooking a VERY common use case - especially in HPC and other systems NOT running on my desk/lap.