Shallow-frying save used much much less
oil than deep-frying.
Food have to move often to cooked all side. Time taken to cooked
will be slower than deep-fried. Chinese chef at restaurant have
a wok with hot oil all the time for deep-fry purpose. But at
home it not practical.
When to used shallow-frying. When you need to deep-fry small
amount of food. Like a few meat ball in the image. Fish fillet,
steak, meat piece are some example.
Not all types of deep-fried recipes can used shallow fried method.
Batter food are not sutible.