Skyrim had the weapons and shields that never clean up.
Ash piles at static locations such as the ritual stone will remain or radiant encounters such the the aspiring mage and forsworn ambush will remain if you reduce them to ash piles.
Enemies at respawn points would never respawn again if a sabre cat or foxes spawned at that point breaking the respawn point forever.
There is an alchemy bug that made some plants never respawn again and plants would disappear and grow back later.
All of these bugs for me except the alchemy bug was fixed by the USKP.
The alchemy bug was fixed by the flora respawn fix.
Without those two mods I will not play Skyrim those bugs listed above ruin the game for me. I went for a year without playing Skyrim until I got my pc. This was my experience.
I just hope Bethesda takes extra time and care for bug hunting and squashing is Fallout 4 and future TES games.