I've seen a lot of house rules adopted over the years by DM's not for balance reasons, but because they were supposedly more "realistic". And D&D doesn't generally handle those well, because the things it tends to gloss over aren't really that much fun to begin with.
Take specific injuries. Someone might say "isn't it odd that you can't lose limbs or an eye, or get scarred by D&D combat?". Then they might decide to add rules for such.
This (at least, from what I've seen) generally leads to either a sorry looking batch of characters who, by the time they are level 5, are all missing limbs, eyes, ears, and noses OR (depending on how they arrive at specific injuries) actually giving players ways to circumvent hit points as a means of defeating foes ("I make a called shot to X!").
I'm reminded of my friend who was gushing about the glory of Runequest: "So I made an attack with my axe, and I hit his arm, went through his armor, went through his arm, went through this torso armor, and killed him!"
"I see. And these rules apply to players as well?"
"Huh? Well of course!"
"Think I'll pass. I already play D&D where I can spend more time buying my starting equipment than it takes for my 1st-level character to die. Anything more extreme than that seems masochistic."