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.
Turn blinds up or down for privacy.
When the blinds are turned up the rounded side faces outward.
It gives you better privacy.
Blinds turned down it may make it easier for peeps to peep in.
With the blinds facing up the inside appearance may not be as appealing as when they re down but you reap greater privacy benefits.
However having the rounded side facing out may not be as aesthetically pleasing as when the rounded side of the slats faces in.
For heat control for summer.
Tilt them down and the blinds look softer and arguably better.
When the blinds are tilted down they could look pretty aesthetically but they provide less privacy as it creates larger gaps between the slats.
When the blinds are tilted up they allow better light control in the room.