Why are overleveled items bad? (Loot Filter question)

I'm trying to implement a loot filter and reading the description for "Overleveled Items" says it would hide them. Why is that?

"During the campaign the itemfilter will remove normal (and on higher strictnesses magic) bases that are completely overleveled and no longer have a good use case."

How do these no longer have a good use case? Wouldn't an overleveled item be good?