I'm wondering if there are any advantages to having a room stat for
this boiler.

There is a legal requirement to have one fitted for energy efficiency
reasons (at least for new installations and replacement boilers), unless an
alternative form of "boiler interlock" is provided. However, any installer
specifying a 24kW combi sounds like the sort of cheapskate that wouldn't
even know what a boiler interlock was.

Without one, your boiler will be churning away wasting energy even when your
house is hot.

Christian.