The joke is you're using the banana but you didn't actually want the gorilla, much less the whole jungle. E.g. you might have an object that represents the single database row you're doing something with, but it's keeping alive a big result set and a connection handle and a transaction. The same thing happening with just an in-memory datastructure (e.g. you computed some big tree structure to compute the result you need) is less bad, but it can still impact your memory usage quite a lot.