My experience with them is for saltwater. Tie your main line to a 3-way swivel, duo snap a bank sinker on one eye, 24" or so leader off the 3rd eye with you hook/bait on it for drifting on the boat. I know guys that use a rig like this fishing from a Dam for Flathead catfish near me also. They will cast and just bounce the rig down current off the bottom, reel back in and do it all over again.
Some use it to toss bait and just soak it. Use enough weight to just hold bottom. I love them people, I don't worry about them putting a dent into the Flounder population. They toss their bait into the water, sit down and read a book for half an hour.
Some use them from the boat to just get the bait down in the water to drift, but lite enough that you don't hit bottom on the drift, just suspends it during the drift.