Most important notes in chords

[jancivil]

as a practical matter of physicality. the amount of energy, for instance of volume, determines how much doubling you can get away with before it gets thick and/or muddy.

the power chord of heavy rock omits thirds because it's already present as a pronounced fifth partial with all that gain, and in fact adding the (13.7 ¢ sharp) tempered major third, with its harmonic series - "distortion" - is a pretty harsh sonority.

once you get out of trad a ways in jazz practice, you get enough movement, additionally you have voice leasning or implications of voice movement so that a lot of P5 gets to be clunky.

we must ask ourselves first, are we talking about an orchestra, a small group, a pianist or guitarist comping behind a singer, a piano bar person, is there a bassist, etc.