setting parameters for functions and nested functions

[mepyyeti]

SO with the 1st snippet:

def foo(bar):
    a = 'moo'
    print(a)
    bar()
 
def bar():
    print('bar function')
 
if __name__=='__main__':
    foo(bar)
else:
    print('choosing not to run')

since both foo() and foo(bar) work to execute the script...is it simply a matter of best practices to just use foo(bar) to run the script? Technically, whether or not I have a parameter doesn't seem too matter...

Regarding the snippet you wrote:

import random
 
def coin_flip():
    return random.choice(('head', 'tail'))
 
def user_choice():
    command = input("Choose Head or Tail: ").lower()
    return command
 
def result(coin_flip, user_choice):
    ''' Doc string explain what function do'''
    coin = coin_flip()
    choice = user_choice()
    if coin == choice:
        print(f'\nComputer <{coin}> You gussed <{choice}> which is correct\n')
    else:
         print(f'\nComputer <{coin}> You gussed <{choice}> which is wrong\n')
 
def menu():
    while True:
        print('(1) Coin flip game')
        print('(Q) Quit\n')
        choice = input('Enter your choice: ').lower()
        if choice == '1':
            result(coin_flip, user_choice)
        elif choice == 'q':
            return False
        else:
            print(f'Not a correct choice: {choice}')
 
if __name__ == '__main__':
    menu()

user_choice() clearly creates a variable, command, and gives it a value but necessitates no parameter. Yet, result(*args) also creates variables,coin and choice, and gives them the returned value of the 2 executed functions, coin_flip and user_choice.

why not just say:

...
def result():
    ''' Doc string explain what function do'''
    coin = coin_flip()
    choice = user_choice()
...

the logic works fine for

...
def user_choice():
#yes I know value of command is set to user's input not  the return result of a previous function
    command = input("Choose Head or Tail: ").lower()
    return command
...

Question boils down to : Why do I need to set up parameters at all. user_choice() shows that I can create variables without parameters (technically just 1 positional)? this is where I get tripped up...