When the blinds are tilted up they allow better light control in the room.
Turn blinds up or down for privacy.
Blinds turned in this direction offer more privacy and light control since the convex side faces the window blocking light or views from the outside.
This may be a good strategy for the winter when you want to warm the room.
With the slightly rounded side facing out and the concave side facing in you have better light control in the room with the blinds up than if you were to turn the blinds to face down.
For heat control for summer.
Tilting the window blinds down directs light and heat into the heart of the room.
When the blinds are turned up the rounded side faces outward.
Tilt them down and the blinds look softer and arguably better.
However having the rounded side facing out may not be as aesthetically pleasing as when the rounded side of the slats faces in.
When the blinds are tilted down they could look pretty aesthetically but they provide less privacy as it creates larger gaps between the slats.