In addition to saving, validating and announcing valid transactions to other nodes, master nodes also perform other tasks with the blockchain including ensuring smooth protocol operations, governing voting events etc Next to validating, saving and broadcasting transactions, master nodes sometimes also facilitate other events on the blockchain-dependent on their nature, such as governing voting events etc. For their dedicated service, they are heavily incentivized. It typically depends on the type of cryptocurrency but Dash, PIVX, Blocknet, Stakenet, and Zcoin are the 5 major coins that have the best incentives for a master node.