Hardened valve seats - do they really matter?

If I go thru the effort to yank a head (or set of heads) they WILL be sent thru a machine shop before they go back on.
The last /6 I built I had OS valves put in, and milled 0.070.
I requested new seats/ at least for the exhaust side, and when I got a call saying the head was done I asked if they'd replaced the seats and they tried to tell me "it's done, oversized seats cut in, everything". I asked again if they put new seats in and was told that they didn't, I insisted they do so before I picked it up, they weren't happy but they did put them in/ took a day to get and a day to put them in.