The setting influences whether Roon will perform MQA Core decoding for the music you’ve chosen. If you desire non-MQA albums from Tidal, you’ll have to select non-Master albums.
As our member @GoldenSound states here you won’t actually get unmolested Redbook, I’m afraid.
So, more compromise to swallow for domestic peace’s sake…
TLDR: Tidal ‘HiFi’ is not lossless. It just streams the MQA version of tracks with some metadata removed to prevent most DACs from recognising it as MQA and limits streaming to 16 bit