Weightless Dragon Bones and Scales
As you progress through Skyrim Special Edition you'll battle various dragons. After you defeat said dragons you'll be able to loot them for their bones and scales. These items are required to make some of the game's best armor.
Problem is, these bones and scales are extremely heavy. Specifically, Dragon Bone weighs 15 and Dragon Scales weigh 10. Looting them isn't a problem if your bags are completely empty but your bags are rarely empty in Skyrim.
If you find yourself over-encumbered in the middle of nowhere you'll need the proper potion or drop some of your precious items to gain extra space.
Or, you could simply download this mod and never have to worry about the weight of Dragon Bones and Scales ever again.