Any down side to hardened seats on cast iron heads?

[jjvites]

Curious as I recall about 8 years ago when my heads were redone at a local shop they installed hardened seats. I didn't think about it much until now except I have always had pinging at lower boost 14 to 15 psi on 91 octane fuel. Any chance the seats are causing some of this. I never hear of anyone using them here.

Thanks,
Marty