Although the baits you mention do cover more water in less time than most soft plastic presentations, I don't consider what they do as searching out fish, or eliminating water. Their use will help you become a more versatile angler as you will learn to fish the entire water column (top to bottom) with the best tool. I'm sure you've had occasion to hook fish as your T-rig was falling, or as you were reeling it in to make another cast. Those were times when the most productive presentation was not on the bottom and although you were able to pick off a fish here and there, a crank or spinnerbait may have been a better option. Then, too, there are occasions where a hard bait will outproduce a T-rig when fished on the bottom, just as there will be times when a soft plastic worked through the upper or middle part of the water column will out produce a 'hard bait.'
These baits can be fished slow or fast. A deep diving crank can be worked slowly on bottom, or somewhere above it. Switch to one that runs a little shallower, or to heavier line and you can burn it just off the bottom. The same can be said of spinnerbaits. A change in weight, blade size/shape, or line can yield the desired speed/depth control that you desire.
If there is one tip I could pass along; avoid a steady retrieve with these baits. A stop and go, or a twitch of the rod tip will outproduce, a methodical 'chuck and wind' retrieve, especially if you're not bumping them into cover or off the bottom.