The Rule of Least Power leads people to lock themselves into low-power languages, only to find that they need more power, which leads to extending the language

The Rule of Least Power leads people to lock themselves into low-power languages, only to find that they need more power, which leads to extending the language incrementally to support incrementally more power, which inevitably leads to a mess. Most heavily-used file formats (even "config" formats) eventually evolve into turing-complete languages, but inevitably they are bad languages, because they were not designed with this end-state in mind.