Very easy to adjust preload on bearings. Can remove bars from stem without removing controls. Can easily adjust reach by changing stems. The advantages seem to outweight the disadvantages to me.

When I built up my vintage Falcon, which has threaded steerer, I had to try three stems before I found one I liked. This involved unwrapping the bars, removing controls from bars, changing stems and then reintalling bars and controls.

On my Trek, remove the top cap, loosen pinch bolts, remove face plate, swap stem.