Wider blades force the paddler farther over the canoe rail, narrower blades require inordinate length to catch enough water. Blade surface must match the individual paddler's size, strength, conditioning, and cadence.
Larger blades transmit more power to the water through increased resistance to blade movement.
This translates to greater acceleration, faster turns, more secure braces, and greater stress loading on various body parts. Freestyle's slower cadences limit stress, but the paddle that provides forward power and secure braces at thirty strokes a minute stresses the paddler at a cruising cadence. Use a smaller blade when it's time to move out. Blades are subtly shaped to perform efficiently. A proper blade needs sloped, or relieved, shoulders, allowing the blade to pass under the canoe during the center portion of a forward stroke.