Braided Line and a leader?

[B.D. jR]

I was at dicks sporting goods and I was talking to a pro bass fisherman who was very knowledgeable about a great many things. I was asking him about braided line on spin and bait casters. He said it was the greatest thing since peanut butter. I have always fished monofiliment but when he showed me the diameter of the 30lb test braided...I could not believe it. He also said it has NO memory at all and made -birds nests- almost a thing of the past. I told him I was interested in catching bass only and did most of the fishing in heavy cover. He talked about using braided line and a florocarbon leader. The PROPOWER braided line looked almost the same color as the -Low Vis Green- Stren. IF the Pro Power 30 lb test is smaller than 17lb test monofiliment why would I use a florocarbon leader?? Are there any circumstances that I would need to use the florocarbon leader? If so, what knot is good to join the mono with the braided. And is it necessary to use a different knot while tying braided??