The ability to load recompiled code on running processes makes it possible to change live services on the fly. I worked for a low budget mobile operator in SE-Asia where there were no test platforms, and every change was on the live servers. Erlang made changes fast, as small changes were trivial, while large changes were broken down into small changes, implemented individually, and tested. Rolling back was fast, as I kept the original code before modifying. No convoluted build structures, and praying the rollout to production doesn't throw unexpected errors.

Programming languages stress reusable code, where you get reusable processes (eg interface to the SMSC)in Erlang, which you would need messaging servers in other languages.