Yes, it's 'easy', but because braces are usually no more than 4x - 6x, they aren't heavy enough to be held down when the mill head comes up from the bottom to cut the curve. This results in the timber being pushed up, even out of the clamp sometimes, and hurdling across the room.
Also, lets say were cutting a brace 4x6x3'. That brace then has a curve which is 3 1/2" wide at the center. Now imagine taking out that extra 2" with a planer, for that's really what the mill head is. That's why we take it to the bandsaw!