Turning big tires takes some work, and steering big meats down a trail all day can work either your arm muscles or your power steering system. Stock steering works fine for stock tires, but adding rubber may mean improving your steering setup.
Going from manual steering to power steering means you can take advantage of some of the engine power to route pressurized hydraulic fluid to a power steering box and increase the steering force. This makes it easier to steer but also has the ability to place more strain on your framerails and steering components.
There are other ways to enhance your steering power, save your arms, and keep from overstressing the frame. The addition of hydraulic-assist steering adds a hydro ram to help push the steering rods and gain you more mechanical advantage. This takes some loading off the frame and gives you even more steering power at the tires.