I believe the grandparent is talking about second strike capability. The idea is to have enough that the enemy can't destroy it all before you have a chance to react. It is possible that one is enough or it maybe that ten is far from adequate. It depends on your threat model.

Not that any of this matters if our threat model includes an enemy who doesn't care if they get annihilated in the reprisal.

Disclaimer: I don't know about any of these things and they are just guesses.

https://en.wikipedia.org/wiki/Second_strike