Hardened valve seats - do they really matter?

Well, that I know of they didn't do any guide work on any of the heads I have sent them, though I tell them every time to go ahead and do so if there's ever a question about them being good or not. So far they've all come back "good" on the guides. They did have to open up the ones on my EQ heads that I took them that were sticking brand new out of the box.... Heads That ruined my last 360 mag rebuild because valves kissed pistons and had to come out again with a whole 6 miles on the job. Those heads are now on another engine with so far 60k miles since they went thru that machine shop