The Horn Section Is a Second Chorus
A horn section is an absurd thing for a small band to want. Three players, three cases, three plane tickets, and a sound that a keyboard could approximate for free before the van is even loaded. Bands keep wanting one anyway. They are right to.
What the Horns Actually Do
The lazy explanation is that horns add energy. They do, but that is a side effect. The real job is answering. A vocal melody states something; a horn line can restate it, a third above, with a different attack and a different decay, and the listener hears agreement. It is the oldest trick in gospel and soul and it survives because it works on people who have never thought about it for a second.
Crucially, horns breathe. A synth pad holds a note indefinitely and the ear eventually stops believing it. A trumpet player runs out of air, and the tiny crescendo-then-fade of a held note under pressure is information: somebody is doing this, right now, and it costs them something. That is why a two-bar horn stab can lift a chorus further than a wall of strings.
Writing for Three, Not One
The craft is in the voicing, and the mistake is unison. Three horns playing the same line are a loud single horn. Three horns playing a chord — say trumpet on top, alto in the middle, trombone holding the root — become an instrument that does not otherwise exist, and the band suddenly has a second chorus available any time it needs one.
Good arrangers also know when to leave the horns in the case. The strongest horn arrangements on record tend to be the stingiest: nothing in the first verse, a single answering figure in the second, everything in the last chorus. Hold them back and their arrival is an event. Use them everywhere and they become wallpaper with a brass finish.
Listen for the Breath
Next time a chorus hits harder the third time around, check whether something brass just joined. Then listen past the notes to the breath underneath them, the small human effort of a player filling a bar and running dry at the end of it.
That effort is why the section got hired instead of the plugin. It is worth the plane tickets.