What Is the Purpose of Setting a Minimum Fee in a Blockchain Protocol?

The primary purpose of setting a minimum fee in a blockchain protocol is to prevent denial-of-service (DoS) attacks, often referred to as transaction spam. By requiring a non-zero cost for every transaction, the protocol introduces an economic disincentive for an attacker to flood the network with useless data.

Additionally, it ensures that miners receive at least a minimal compensation for their work in validating and securing the transaction. This mechanism protects the shared, scarce resource of block space.