I highly doubt it's useful these days on general purpose computers, where even the very smallest ones can easily implement C (or better) or even run a whole operating system like Zephyr or Yocto.

However if you're creating your own computer from scratch or have other artificial constraints (like it needs to fit into a boot sector[1]), and if you want to really understand precisely how your language works down to the lowest level detail while still having high-ish level constructs, then Forth is the ideal small language for that.

[1] https://github.com/cesarblum/sectorforth