Much stronger than make_ref/0 (64 bits vs 122 bits, which with birthday collision will provide 10¹⁰ difference factor in possible collisions). And generating UUID can be done also outside of the BEAM, which is clearly a win for me.

Don’t expect to. A reference is just a marker to a “place and time”. They’re usually otherwise empty values that are “guaranteed” to be unique. Now, sometimes they are coopted by the vm to refer to “something” but by and large they aren’t references like references in the JVM.

For example, let me send a call to another process. When the response comes back, it should somehow refer to the initial call, so that this response isn’t structurally confused for a callback for some other call (that maybe got dropped and thus orphaned). The thing that the call sends, which should be packaged with the response, so that it can be can referred back to correctly is a reference.

make_ref()
|> :erlang.ref_to_list()
|> List.to_string()

Remember that references are meant to be unique only within single cluster, there is no guarantee for global uniqueness of the reference, in contrast to UUID.

Elixir and Erlang libraries mostly use binaries for storing UUID which IMHO makes most sense.