Why do you need a network mask?

In the realm of cryptocurrency and network finance, one crucial element often discussed yet often misunderstood is the network mask. Could you elaborate on why a network mask is necessary? What role does it play in securing transactions and maintaining the integrity of the blockchain? I'm particularly interested in understanding how it impacts privacy and security, given the sensitivity of financial transactions. Furthermore, are there different types of network masks, and if so, how do they differ and which ones are most suitable for specific applications? Your insights would be invaluable in clarifying this crucial aspect of cryptocurrency and network finance.