On Windows Phone 8.1 you could configure one or more calendars to toggle quiet hours automatically. That feature is absent from Windows 10 Mobile and therefore quiet hours is virtually useless for me.
Another feature that was removed for unknown reasons is browser data savings, which is mildly infuriating.
All in all I'm very disappointed in Windows 10 Mobile bceause on the one hand it comes with very few advantages over Windows Phone 8.1, but on the other hand a major step backwards for many different reasons too, actually for the above two reasons alone. I'm not going into detail here, because this has been discussed many many times.
The ship is sinking and I don't believe there is any way to stop it at this point.