When getting the boat on plane, for instance, lowered tabs create substantial lift to raise the stern faster, so you're off and running quicker. That is often a big concern in small boats like flats skiffs in situations where you have to jump on plane in a short distance. Cavitation-plate extensions offer the benefit of placing lift in the farthest aft spot possible, so that the greatest lift per square inch of tab surface is achieved. Tabs enable you to correct for unbalanced loads and help keep the boat on plane at slower speeds, a major benefit when you're offshore and trying to make headway through rough seas. Normally, you have to slow down to keep from pounding, but when you do so, the boat wants to fall off plane as the stern settles.
Tabs help the boat run level at slower speeds, which also helps maintain unobstructed visibility.
It's dangerous to mush along at slow speeds with your bow high in the air. A level running attitude lets you keep a lookout in all directions. You can also run faster into a chop in an outboard boat by experimenting with a combination of trim settings involving both the tabs and the engine outdrives. By setting the tabs down somewhat, and then trimming the outdrives up slightly, you can make the hull ride perfectly level, and it's amazing how much faster you can run in a short chop after trying different combinations of the two trim adjustments. And when the outboard's props are providing thrust parallel to the water's surface, efficiency is enhanced, too.