Expo works both ways. Most common is to soften up the center (less movement for the amount the stick is moved). Or it can be the opposite. Some radios expo in the negative slows the movement others it’s positive I don't know why it’s not standardized. Expo is great when using large control surfaces along with great movement it can be set up at centre to reduce the action of the control surfaces for general flying while keeping exaggerated control throws for wild aerobatics.