The benefits teeter from good to bad - non scientific guesstimate, at 3 balls you're probably sailing. At 4 balls, you're looking at long banks and cuts to start on.
Also less defensive cover.
19 might be the sweet spot for moving the ball - perfect rolling etc... 20 seems to default to stun/stop. Below 19, you need to create stun and stop shots.
Course that's just my default bridge, stroke, and preferred strike locations.