Oh, it could be anything really. It is more about establishing your "ruling" for future use and it standardizes it for new players, so they know what to expect in those situations.
ruleings that I kept and then kicked myself for...
can things stick to an invisible opponent and make them visible (there is no right answer, just PCs complaining or abusing)
Can you target a rope with a ranged attack
how flammable is (fill in the blank here)
in an enclosed space can fire eat oxygen and as such suffocate things
how athletics checks interact with jump
how acrobatics checks interact with fall
if you know a language that uses the same alphabet as another one can you read both?
can you train a (fill in animal here) like this youtube video shows can be done in real life?
can you pull some ones ear off with mage hand (this one DOES have a right answer...no)
what parts of the armor are needed to get the AC, and what parts give you disadvantage (NO I don't want porn plate...)
If I am enlarged, and I pick up a large weapon it still does large damage but my weapon enlarged doesn't... how does that work (God insert pym particle mubo jumbo here)
can you teleport/dimension door a creature I am grappling to a height and drop them?
how does CPR work on death saves
by the way. this isn't 'every house rule/ruleing' not even close... this is last month of 2 games a week