How Does a High Volume of Zero-Fee Transactions Affect Network Congestion?

A high volume of zero-fee transactions can contribute to network congestion if the block space is limited and they displace higher-fee transactions. However, in a competitive environment, miners will generally prioritize higher-fee transactions, leaving zero-fee transactions to languish in the mempool.

If a miner chooses to include them, they occupy valuable block space that could have been used for higher-value, higher-fee transactions, effectively increasing the average waiting time for others.