[bpfrh]

Depends on the nato country, but most only use if attacked, which makes perfect sense as these where times where the most dangerous country was the udssr for them.

If you where a nato country you had the problem that by the time reinforcment from the usa could arrive, the udssr could potentially be in control of most if not all of europe.

While the udssr didn't really had that concern, as they had more than enough room to retreat, reform and defend.

In such a scenario it's very easy for the udssr to have a no first strike policy when there was simply no way for any european country to invade them, while smaller countries would have had a real concern that they either use their weapons to the full effect or have no chance to do so.

IMHO there is also the substantial benefit that the udssr now knew that any attack meant that they would trigger a war without winners, e.g. they couldn't fight and then retreat to safe bases deep in their territory