1. You can cover more water with less time. 2. You can throw further out with the spinning rod. 3 You can easily manage the depth of your presentation with the bubble. 4. It is easier to use when it is windy . 5 and last but not least I can sit on my rear cast all day without working at it.
Lots of the above can be negated by fishing from a floating device however I don't prefer them.
Tim