It is very good :) let’s just say that developers build software but need a way for the software to communicate with the blockchain, the rpc nodes allow this to happen, kind of like a “middleman”. Faster nodes mean developers can create software that can handle more users and more transactions, kind of like @steemvoter and @minnowbooster, which process lots of transactions.

Oh and a cluster just means that there are a few nodes working together, so if one fails the others still keep running, also when all three are up means the power of all three are combined to serve even more transaction requests.