Inventory Management. Doesn't matter what game it is. If you can get over-encumbered and it's not relevant to the game play like a survival crafting game or something I fucking hate it. There's no reason I should have to make 40 trips to pick everything up in a Skyrim dungeon if I want to. It just wastes time.
In a similar vein on skyrim, what's the point of having merchants have limited money when fast travel/wait is a thing?
All it does is make me spend 10 minutes fast traveling to all the towns to sell my stupid dragon bones. What does that even add? It doesn't add difficulty or immersion. Because of the dumb encumbrance, I can't continue playing the game until I sell all this crap, so I gotta deal with it sooner or later.
Guess I'm the weird one. I regularly use mods which give me less carry capacity and add other restrictions and such realism mods. Like, you don't have to take everything of value. It always felt weird to me that level 1 chars can carry like 300lbs/kgs/whatever of junk around and still fight effectively.
I suppose this falls under the realism category. No vendor in a "real world with fantasy elements" has infinite money and buys everything from you. And in the early game you can't fast travel everywhere.
Combine this and you get a reasonable game mechanic that restricts too fast player advancement in especially the early game.
Later on you can develop a skill that lets you sell to every merchant.