What is the purpose of a freecell pile in solitaire?

The purpose of an empty pile (free cell) is so that cards can be reorganized more easily. Switching cards to the empty cell as an intermediate step opens the game up a lot, in a lot of Solitaire games, including the one called "Freecell." There are hundreds of kinds of solitaire though, and in some games the empty piles can't used anymore, or the empty piles can only be filled by specific cards, which limits the advantage of having those blank spaces.