Main reason you would probably be better off with a leader is that braid is less than ideal with respect to abrasion resistance. Consequently, mono is less abrasion resistant than fluorocarbon. So, if you are fishing sub-surface, I'd recommend a fluorocarbon leader vs. monofilament. Unless you are fishing top waters. Here, monofilament has the edge due to it's floatation characteristics, whereas fluoro has a tendency to sink more rapidly. And this holds true regardless of the species you are fishing for.
Tie the lead to the braid via an Alberto knot and you're good to go. I'd use at least a 3' section, as this will afford you a bit of shock resistance as well. Fluoro does stretch, regardless of the claims of some manufacturers. As a side note, mono stretches even more than fluoro. A side benefit of a fluorocarbon leader is it's near invisibility under the surface. Another plus, although not the primary reason for using this material as a leader.
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