Just an alternative viewpoint: Personally I really like the ghost reviews so I leave them on the ‘On’ (the default) setting, rather than ‘Minimal’ or ‘Off’.
What I like about them is that by adding extra reviews to my pile, it gives me a cue to slow down: Taking more time with individual reviews so I don’t make careless mistakes; but also slowing down on starting new lessons (Study feature), so that I don’t get overloaded with too many grammar points that are too new-to-me, i.e. one’s that I don’t really ‘get’ yet. [And they only last for 4 SRS levels, so they don’t burden you forever; plus you get extra badges for banishing ghosts! ]
Anyway, that’s just my personal style of learning. I could easily understand why others might not like the extra, repetitive reviews. For me, they’re great, though!