For each aspect the player needs to define a positive effect, which is usually a situational modifier to certain tests. For example, a knight's 'Faithful' aspect can provide bonus dice for fear checks. To activate this effect, the player needs to spend Story points.
Each aspect can have a negative effect, which is usually also a situational modifier to certain tests. Expanding the previous example, the knight's 'Faithful' aspect can be used by the storyteller to offer the player story points in return for dice penalties for the scene.