The Austin tower would allow better system talk-in for portable radios in the Austin vicinity. Usually state wide trunking systems are designed for "open areas". They don't provide real great coverage for larger buildings such as hospitals, shopping centers and warehouses.
So local municipalities are "on the hook" to provide additional sites to provide coverage to these concrete/steel structures. Minneapolis, Hennepin County, Ramsey County, Duluth and St. Cloud are good examples of these. If the community is "sprawling" you'll often see these "sub-systems" as simulcast systems.
Also another benefit of a local tower would be a greater number of voice channels available for use.
There is a wealth of information on the Minnesota State Radio Board's site and makes for good reading if you have the time:
https://dps.mn.gov/entity/srb/Pages/default.aspx