In what situations what you use DACUS to do a true combo? I don't think I've ever tried it outside of punishing on-stage recoveries and tech chasing.
Like Y-L said, DThrow -> DACUS can be a true combo on floaties depending on DI,
even at high %s. If they DI in on FThrow or BThrow it's possible to land a DACUS, as well as out of UThrow
on spacies. Reverse NAir -> DACUS is also a true combo with no DI around 75% on some characters (IIRC it's around 80% for TL), and you can also NAir -> DACUS depending on DI. Key disclaimer for most of those things is "depending on DI" though, so it either requires a hard read on their DI, quick reactions, or purely YOLO'ing. On Fountain, you can either NAir or throw opponents onto low platforms and then DACUS to cover all four of their tech options (missed tech, standing tech, and both rolling techs), basically making it guaranteed when timed properly.