For most trail riding, 200mm rotors are more than you need—180mm front is the sweet spot there. But if you're riding steep, sustained descents on an enduro bike or you're a heavier rider (over 180-200 lbs), 200mm rotors up front are a smart choice, not overkill. The larger surface area gives you more stopping power and dissipates heat better on long downhills, which means less brake fade when you're on the brakes hard for extended periods.
A common setup for aggressive riding is 200mm front and 180mm rear, since your front brake does the majority of the stopping work. Just keep in mind that upsizing to 200mm requires a compatible fork mount, so check that before making the switch. It's one of the most cost-effective braking upgrades you can make if your riding actually calls for it.