Watch the Placement of Important Chords online guitar lesson by Matthieu Brandt from Songwriting on Guitar
In any song the I, IV and V chords will be the most important, wether the song is in major or minor. Some songs do away with using the IV or V, but in a general sense these chords are the building blocks of a well written song. Placement of these chords influences the overall feel the song or a song section has. The perception of balance or forward momentum (tension) is influenced by where and when you use these chords in your composition. The I chord will give you a balanced 'home' feel in a major key, but the VIm chord also has kind of a home feeling. In a minor key the III chord has a similar home feel as the tonic chord.