Well, for 8-ball and 10-ball I definitely prefer breaking from the table bed, right at the balk line. Yes you're getting the ball closer to the rack when you bridge on the table. But more importantly keep in mind that since you usually want to hit the cue ball ever so slightly below center to control it on the break, bridging with your hand on the table bed lets you reach the bottom half of the cue ball while keeping a more level cue than if you were bridging off the rail. If you're going to try to hit bottom CB breaking off the rail, you either have to use a very long bridge length off the rail which is very easy to lose control of, or you have to elevate the back of your cue which makes your break much less efficient.
Of course, it's more common than not to bridge off the side rails for 9 ball and sometimes 10-ball. Or if you feel like trying to make the 8 on the break, you can bridge over the side rails. But bridging off the side rail is done to get an angle to pop in wing balls, not for power.
Basically if you're shooting a rack of 10 or 15 balls you probably want to break with your hand on the slate so you can more comfortably control the CB and make sure it lands in the middle of the table. If you lose control and accidentally force-folllow into the rack, you can really hose yourself.
All that said, I could see that depending on your break form, how tall you are, and how long a bridge length you use on your break, you might break from the back rail on a 6-foot bar table. If you tend to take a BIG backswing on the break and raise up on your final stroke, the kitchen on a bar box might not be big enough for you to comfortably bridge off the table bed, but I think that's rare.
Even the heaviest legal break cue is 1.5 pounds, it doesn't take much to get it moving quickly, and getting a 25mph break off the table bed is within the physical capability of most people. Okay yes, a lot off top players have developed elaborate breaking styles to get every ounce of power they can but you'd be surprised of those diminishing returns, how much more you have to do for ever-smaller gains in power. The normal pool stance is a bit sideways, and that helps us get a longer stroke with more time to accelerate, involving the hips and body a bit more to snap through. However, if you stand with your hips and shoulders more square to the table with your feet nearly side-by side shoulder-width apart, as in a snooker stance, all the joints in your arm and shouldere actually line up in a very efficient configuration, like a softball pitcher, and it's really quite amazing how much controlled power you can generate in a very short stroke with little to no body movement. It's worth trying simply because it's easy and reliable, a nice fallback when your big windup break isn't working for whatever reason.
