Extra-wide platforms expand the contact surface between cleats and pedals, for efficient power transfer and a solid feeling when you stand on them. Whatever your road-riding level, these are good things.
Red SPD-SL cleats have no float and are 100% fixed in position. This makes them great for sprinters, professional athletes, or people who value the most efficient power transfer possible and are not prone to knee pain.
Yellow SPD-SL cleats are perhaps the most popular among casual fitness cyclists but are used by a wide range of athletes. They're characterized by a six-degree float range, which allows for free movement and low joint stress.
Blue SPD-SL cleats are Shimano’s newest cleat option and they exist as a middle-ground between yellow and red. Blue cleats have two degrees of float, allowing for a small range of movement while still delivering a high amount of pedaling efficiency.