What is the real difference between mixins and functions?
Work the same. On what moment I need to use functions vs mixins?
They can serve the same purpose and often can be interchangeable, as with many things in programming, the answer is use logic. Even though they may serve a similar function, their purposes are a bit different. Mixins are used more for includes and functions are more for returning values. The sass way has a nice write up on the two.
Hope this helps.