1 Basically it can repeat a function.
Looping control flow allows us to go back to some point in the program where we were before and repeat it with our current program state.
2 Loops repeat code. They are usefull when require to do a certain function (task) several times. Like counting from 0 to 100 in even numbers.
3 A do loop will execute code at least once and then looks if it should repeat that code again. A simple while loop will not execute once if the a statement is false.
4 Aesthetics. Sturcturing code in a way that is easier to read for the person viewing it, without changing what the code does.