Is /usr/local a per user folder? Is /usr/local a per user folder?

homebrew says

/usr/local/bin
/usr/local/etc
/usr/local/include
/usr/local/lib/pkgconfig

This can happen if you "sudo make install" software that isn't managed
by Homebrew. If a formula tries to write a file to this directory, the
install will fail during the link step.

You should change the ownership and permissions of these directories.
back to your user account.
  sudo chown -R $(whoami) /usr/local/bin /usr/local/etc /usr/local/include /usr/local/lib/pkgconfig


Doing so would make those folders belong to a particular user which would mean another user using the same machine would be S.O.L. unless those folders are some magic per user thing.

Are they? They don't seem to be at a glance but I probably don't know how to figure out if they were.
No, /usr/local is not a per-user folder. It's the same directory for all users. I've been down this road with homebrew and done the chown to /usr/local on a laptop that only I use, but my other non-homebrew-aware Macs all show permissions similar to this for /usr/local:

%ls -ld /usr/local

drwxr-xr-x   213 root     wheel    578 Aug 28 11:58 /usr/local


And they work just fine like that.