For most mountain bikers, 220mm rotors are overkill. These massive rotors are designed specifically for downhill racing and extreme terrain where you're bombing long, steep descents that demand heavy, sustained braking. They deliver maximum stopping power and the best heat dissipation available, which helps prevent brake fade on punishing runs.
The trade-offs are real, though. 220mm rotors add noticeable weight to your wheel, and they require compatible fork and frame mounts—not all bikes can even fit them. Most trail and enduro riders are well-served by 200mm front and 180mm rear rotors, which offer excellent power without the weight penalty.
Consider 220mm rotors if you're a heavier rider tackling steep, sustained descents, or if you're racing downhill competitively and need every bit of braking performance. For typical trail riding or cross-country, smaller rotor sizes will serve you just fine.