There are proponents of both styles of bridges. The open bridge allows an unobstructed view of the shaft for aiming purposes. The closed bridge ensures that the stick will not deflect when hitting the cue ball out from the center.
In snooker, with the smaller balls and thinner cue shafts, the open bridge helps aiming at balls up to 12 feet away into pockets a fraction of the size of regular pool tables. All of their shots with and without spin use the same open bridge and long, down the barrel, aiming process.
In pocket billiards, professional level players use a mix of both styles. The majority use a closed bridge. In almost all of the instructional books and videos that are introduction guides to playing, the most recommended bridge is the closed bridge. Part of the reason for this is to ensure that the cue shaft goes forward in a controlled line.
For pocket billiards, it is very useful to be comfortable with both bridges. You will find that an open bridge is useful for long, far away shots. When executing a shot with higher than normal speeds, the closed bridge provides assurances that you can keep the stick continuing with a proper follow-through. For other shots that need a firm delivery, the closed bridge also helps to restrict the path of the shaft.
Which bridge you use will depend on your experience with the open and closed bridges. Even within these two options, you have individual variations that you find useful for your own needs. To get comfortable with both types of bridges, simply shoot lots of shots with both styles.
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