Typically, tunneling involves abandoning the tunneling machine underground because it's too difficult and expensive to retrieve. The Boring Company's innovation was to find a way to retrieve the machine inexpensively, thus significantly reducing the cost of tunneling.

They also operate the machines remotely, so that humans are not risking their lives underground.

Tunnels are a good thing. They cut across a city without paving over more greenery. They will reduce surface traffic.