Cash Drop's free bonus cash lets the player have more gold than normally possible, especially early on. One Gold is generally a low impact draw overall, as the card could be better used for more impactful cards in a deck, and for combo strategies, Quincy Action Figure is much better for supplying extra cash in a single turn.
In older versions, Cash Drop could be used in Aggro to provide an advantage over opposing Aggro by allowing the user to afford more expensive Bloons quicker. In newer versions, due to better anti-Aggro options, Cash Drop sees little use.