I'll come in on the other side of the coin. Where ever possible I have removed "things" that either don't work or I don't like. The seat belt warning buzzers and their harnesses, smog stuff that has long since stopped doing anything. I've taken the side marker lights off, front and rear and their related wiring. Rusted door light switches and their wiring.
The windscreen washers, their brittle, yellowed hoses, it's pump and related wiring were the first to go.
IMHO it makes for a much cleaner engine bay. For fun sometime, download and compare the colored wiring harness diagrams for early cars with a latter car. The complexity is mindboggling.
I know some "modern" improvements have been made. And this is my first rubber bumper car...But there is so much stuff...
But, as has been said. Be careful not to leave loose wires dangling about. In most cases I have opened up the harness and taken the offending wires right out.
I like getting back to the basics of the engine bay.