Major 7th Chords in Film Scoring
Major7 chords (e.g. Cmaj7) are a bit tricky to handle and should be written with care. They are usually used as tonic chords, however function very nicely on the subdominant position as well.
The actually very dissonant major7 in this chord gets stabilized by the third that creates a very consonant perfect 5th with it. However it is still a very “dangerous” interval. The actual danger is a potential minor ninth which could happen at a “unfortune” inversion of the chord which has such a high grade of dissonance that it will dominate your whole remaining chord structure. Even worse is when your melody hits the root note during that chord which is a lose-lose-situation: either it is a minor second on top of the major seventh of the chord which will heavily obscure the melody and make it very ambivalent or it creates a minor 9th (+octave(s)) with the maj7 of the chord. None of this situations is something that sounds great. The common resolution is to swap the maj7 with a 6 chord which has a compareable sound impression without creating dangerous intervals.
In film scoring, major7th chords are stylistically a bit outdated as they have been used quite a lot in the 70s/80s particularly by John Williams. For instance his SUPERMAN theme makes a lot of use of maj7 chords. With this stylistic knowledge in mind, maj7 chords still can create fantastic harmonic worlds when used properly and with care. The mentioned use of a maj7 chord on the subdominant for instance very often sounds very attractive and doesn’t have the dated sound quality of a tonic maj7 chord.