Benefits of Soft, Medium and Hard Curved Ski Board

soft:

beginner
Easy to maneuver and initiate turns
Forgiveness at low speed
park knight
Easy to press and twist to any position you need
Unbalanced landings have more room for error.

Moderate:

most riders
Balance of stability and maneuverability
Adapt to various conditions and terrains
Capable of making some short, quick turns, as well as longer pull-out, sculpts
Suitable for riders of all ability levels

stiff:

More aggressive/hard-charging riders
Very stable at higher speeds
Comfortable sculpting and seaming edges on steep terrain
Powerful transition from one turn to the next

Each flex has its advantages, but there are also some disadvantages worth considering to ensure you get the best flex for you. Softer skis tend to get nervous at higher speeds or technical terrain, they won't feel stable and won't lock into the snow. Really stiff skis can handle this faster, more technical riding better, but require more effort from you (the rider) when cornering at lower speeds. Most riders will probably find themselves somewhere in the middle, wanting a ski that is stable when riding faster and can run a few laps without feeling like they can't turn the board.