Yeah I agree I thought that many people had tried to help. OK to take up larry's challenge:
Reasons not to use elevated bridge for general play:
1) When elevated the cue you end up pushing the cue ball into the slate which will result in the cb jumping slightly. Therefore you have a bouncing cue ball heading towards the object ball although this may not be visable to the human eye. It doesn't take a rocket scientist to see that this is not a desirable way of contacting the object ball. I'm sure most of you know what a kick is, a kick (although the cause is still up for dispute) often results in one or both of the balls in question jumping on impact. This usually seriously effects the role of the cue ball (slowing it down dramitically so desired position is lost) or even throwing the object ball completely offline so the pot is missed.
2) Also ask yourself how do you swerve the cue ball? You jack the cue up and hit on either side of the cue ball. This means that you must take great care to hit exactly the center of the cue ball when jacking up the cue, especially if the obect ball is some distance away. If you hit slightly off center playing with a level cue the amount of swerve/deflection will be much less than have you it the same spot while jacking up the cue.
3) IMO jacking (depending on how high you raise the butt) up the cue also limits follow through (since your not playing parellel to the table) and also effects your aim.
Although I am arguing that you should not use a jacked up cue for general draw shots there are circumstances when its a valuable tool or even the only shot you can play:
1) If the white ball is near the rail/cushion and you need to play a draw shot.
2) If the white ball is near another ball and you need to play a draw shot.
3) Jump shot (but that stands to reason since you would normally play this shot with a jacked cue anyway) etc..
Jump shots raise an interesting point which has already been picked up on. Larry can draw the cue ball while hitting it in the center, but with jump shots you are hitting it at the top. In reality you are always hitting it at the bottom realitive to the direction of the cue.
I would agree with larry that it is probably likely that if it was a pure contest you could probably get "more draw" by raising the butt. Consider what happens when you raise the cue butt. The poor white ball is trapped between two fairly hard objects, one the slate which isn't going anywhere and the other the cue (which is held by strong player eg you

moving at some force towards the cue ball. Now since its unlikely that you will have raised your cue so that is vertical to the table you will be applying a force that it is at an angle to the slate. Now hopefully you can picture these two forces then the poor old cue ball is pinched between two forces with only one place to go. It is forced into the slate/cloth slightly in the direction of the cue force then it shoots out wich creates tremendous spin. Picture hitting one side of the cue ball on top with your hand in a karate chop motion. This is what is happening to a lesser extent when you jack up the cue.
Now compare this to a level stroke, when playing a level stroke there is only one force that comes into play and thats the cue. This shot doesn't create any pinch as the cue ball is played away from slate not trapped between two forces(objects) so all the spin must be created by the cue stroke.
IMO you need both shots in your amoury but if you are just learning draw master the level cue method first. You can get more than enough draw using this method for all your positional needs apart from the exceptions highlighted above. The jacked up method has its uses but they don't include general play.
Hope this helps
Craig