Trying to reason out when 3 notes might do a better work than 4 (again fighting against my now aware bias towards more=better).
3 notes in the mid range, plus a bass note, is super great. 4 is super cool too. if we were to start listening to every song on the planet in random order, and go through and check how many notes are in each chord, in the mid and bass range, i'm pretty sure we would find that by far the most common case is 3 or 4 notes in the mid range, and 1 in the bass. that even includes the melody