Where excluding a hyphen would be likely to lead to a mispronunciation from the word for the reason that "pre" seems to not be an entire syllable (such as, "pre-yaw course", which could be browse as "prey aw class" if unhyphenated). Prefix prepended to imperfective verbs to produce them perfective; https://elliotttafkq.wikicorrespondent.com/6400393/top_pre_owned_louis_vuitton_secrets