When drifting with a spinning reel, the tention on the line while drifting towards you becomes slack. With a centre pin(flaot reel) you can control the amount of slack whether its infront of you are floating downstream away from you.The flow of the river starts the reel moving (inertia) and it will gradully take line off the reel as its needed, thus when your float goes down you set the hook much faster due to less line out.
Also, with a longer rod (STOP RIGHT THERE MIKEY!)..when setting the hook you are picking up more line much more quicky then a shorter rod, thus faster and more immediate hook sets.
Hope I explained this well enough for you.
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