Her'e the kind of semi-scientific reason.
Frying takes place at very hot temperatures. One of its main virtues is the ability to expose every nook and cranny of he food surface to that high heat. That heat draws water that is near the surface up to the surface, becoming steam as it gets near enough to the surface to exceed the boiling point. So the surface can get very dry, since there is a limit to how deeply water can be pulled from. (Remember, although the oil is very hot, perhaps 350 to 450 F, we certainly aren't taking the meat to that temperature. Frying is a hot, fast treatment that takes interior to traditional doneness temperatures for the particular food type.)
A coating of starch, usually flour, quickly forms a crust of sorts that tends to trap moisture and keep the surface from drying too much. Note that we don't dust things like potatoes. They provide their own starchy surface.
For foods with lower doneness temperatures, a batter may be better. Shrimp, for instance, cook quickly, have a high moisture content, and dry out and toughen easily. For them, batter does a better job than just dusting, if frying is desired. You really like the shrimp to steam more than bake within their batter jackets.
There's a mouth feel issue, too. Crunchy/crispy is attractive. The type of coating determines this. Panko crumbs present the hot oil with more surface area, so they panko crust are very crunchy. And visually some foods need a starchy surface to brown attractively. Even lightly breaded okra is far more attractive than plain okra cooked in frying temperature oil. Ditto for onions and most other vegetables, most of which would suffer with unattractive, shriveled surfaces if fried plain.
Chicken liver is a lot like shrimp. No liver will tolerate being overcooked. A coating does as described, trapping some moisture, which created a cooler barrier layer, which still surrounding the food with super hot oil capable of loading the liver with heat deeply and quickly.
As with all frying, the food must be eaten soon after cooking. That same moisture trapping layer makes it quickly turn limp and unappetizing. If you can't eat it quickly, as someone stated, saute instead. The lower heat exposure doesn't draw water so quickly and doesn't trap moisture, so you have a little time to eat it while it stays much as it came from the pan.
I mentioned potatoes as having their own starch coat. They're starchy throughout. There's a serious downside to that. If you try french fries by just dumping stringed potatoes into frying oil, you get dark, limp fries. This is closely related to why you get gluey mashed potatoes by just dumping potato chunks in boiling water and then beating them up. Potatoes have a peculiar cellular structure of starches and pectins, and those cells are subject to being broken and other changes. In the case of mashed potatoes, a short parboiling and cooling stabilizes the cells. Then further preserving the cell structure by ricing instead of mashing or beating makes them smooth.
Crisp fries that can hold their crispness to the table require careful parboiling in acidic water and partially fried and (for best results) frozen before going into the fryer still frozen. (It took McDonald's a LOT of lab work to develop their method.) A lot of work, but happily for you (and for McDonald's) they can be prepped in batches and stored frozen until fried. So the nature of the food does dictate how food must be prepped and fried for good results. And there are lessons in the french fries technique that can be adapted to other foods to help them stay attractive for longer after being fried.
"Kitchen duty is awarded only to those of manifest excellence..." - The Master, Dogen