Globals vs Function

[mcmxl22]

Is using a function like this to define variables ok? 

def variables(a, b):
    a = something
    b = another

def some_function():
    do something with variables(a).
    do something with variables(b).

What is the difference between using a function to define variables and just using globals like this?

a = something
b = another

def some_function():
    do something with a.
    do something with b.