I'll use a single object for, say, collectibles. That way if an enemy drops one I can just spawn the object and set its animation from a list.
However, if the game has a lot of floating collectibles then I'll use separate objects so I can easily pick them from a folder to place in the layout.
For backdrops...it really is preference. You could bundle things like rocks, clouds, plants, etc. but do you want to refer to and type in the animation or frame for every instance? I'd rather have a folder of individual assets to pick from in that case.
If they are usable you might want to bundle them into a single object and use conditions to tell them apart, since you can't refer to an object by name. For example you've got 3 different springs in a family. If you use "Player landed on spring family" then there's no way to tell them apart without a name variable. You might as well just use one object and compare the animation or something.