What is LRC?
LRC is the lyrics format music players read for a synced, line-by-line display - a timestamp in brackets, then the line. It has starts but no ends, so a converter has to infer each line's duration from where the next one begins.
What is ASS?
ASS (Advanced SubStation Alpha) is the subtitle format for people who care where the text sits: styles, positioning, fonts, karaoke timing. Anime fansubs made it standard. Converting it to a plain format means the words survive and the choreography does not.