However, the change has raised questions about council activities that cross over with central government responsibilities, with speculation some will be canned altogether.
Mr Key did not shy away from the possibility today, saying he wanted councils to focus on their core business.
"In narrowing their purpose clause, it may exclude them from providing those services, or at least challenge their thinking about whether those services should be provided,'' he said.
"One has to ask the question, if central government isn't providing those services, then really should local government step in and fill the breach? Because there might be a very good reason why central government hasn't done it.''
Auckland Mayor Len Brown is among those who have questioned what could be lost with the reforms, saying it would not be acceptable if the changes meant a council had to stop plans around social activities, or aspects to the city such as roading or public transport.
Speaking to media this morning, Dr Smith argued that the reforms were not being taken too far.
"The key new test that councils will need to apply in the way that they spend money is that there is a public good,'' he said.
"The current constraints are basically negligible, they can do everything. In my view, there is still a lot of room for councils in the way in which they define those public local services, and the way in which they define that local infrastructure to provide all of the things our communities would want our councils to provide.''
New fiscal responsibility requirements, and plans to allow easier council amalgamations are also among the reforms announced yesterday.