Should I just use min-width?

This is more an opinion discussion rather than an actual question .....

In the video Guil uses both min and max width on a media query. Should it not just be min width, with base styles for the elements at mobile size and then expanding on it using min-width media queries to build on the styles until you reach a desktop layout?

Guils code (or something to that effect):

@media only screen and (max-width: 769px) and (min-width: 481px) {
  body {
    background: orange;
  }
}

@media only screen and (max-width: 480px) {
  body {
    background: green;
  }
}

Should it not be:

body {
  background: green;
}

@media only screen and (min-width: 480px) {
  body {
    background: orange;
  }
}
@media only screen and (min-width: 769px) {
  body {
    background: blue;
  }
}

I guess this is the whole debate on using max-width or min-width in media queries!! :)

In a further video, he does go on to discuss the mobile first approach, which implies that it should of been shown from the beginning?!?!?

This is just out of pure curiosity! :) Happy Coding guys!