MOABs can pressure the opponent at most stages of the game, while additionally supplying Bloontonium.
For Quincy in particular, it is often more reliable than a BFB for efficient Bloontonium. The MOAB's Bloontonium is a factor of 3, which allows your Quincy to send two MOABs to reliably get back to full Bloontonium without overflow, whereas with the BFB its 7 Gold cost is more easy for him to overflow on Bloontonium.
During early rounds, a single MOAB pressures the opponent to use single-target damage to chip it down. For early rounds, it is often best to send one MOAB first and follow up with another MOAB to pile up the pressure, rather than two at once.