Of course your results will totally depend on your trainer but my FTP went up almost 20% the day I got a power meter!
That actually did not make any difference but what did is it turned out my trainer’s performance was not consistent across the total range of power so not only was my power curve off, it was off at different amounts at different powers. So, doing workouts of a real PM ended up being a total game changer. But I think that is a pretty rare occurrence.