The New Zealand Building Code requires that decking on the main access route to a building must have a slip resistance of 0.40. Grip tread timber decking will conform to this requirement.
If not on the main access route then the decking can be installed smooth face up.
To help you make an informed decision, I list below the pros and cons of each option:
Grip Tread (Grooved Face) Up
Better slip resistance (one way only, for travel perpendicular to the grip tread lines)
Interesting aesthetic
Grooved face masks surface checks that occur over time