Primarily..
I primarily use them any time I would throw a soft plastic. I have found them EXTREMELY effective for sight-casting, especially when reds/trout seem relunctant to hit a spoon. You can pitch them out in front of their path and just let it sit, or move it very little. A red passing over it will likely stop, turn around, and begin rooting around until he "gulps" it - even if it is buried in the grass/mud/sand.
That being said, I prefer to catch fish on "hard" baits - sometimes working soft plastics (or corkies) is much too slow when fish are scattered or I'm covering water to find fish. But once you find them, especially when wading, Gulps will catch them when nothing else will.
I have a friend who will throw out a rod and drag one behind the boat while we are drifting and tossing topwaters ahead of the drift. Just be sure to have the rod secured.
OH, I mostly fish the 5" Jerk Shad in New Penny, Peal/Glow, Sardine, or Nuclear Chicken.
They are without equal when rigged weedless fishing the mangroves for snook and snapper.