Longtermism suggests a different focus within existential risks, because it feels very differently about "99% of humanity is destroyed, but the remaining 1% are able to rebuild civilisation" and "100% of humanity is destroyed, civilisation ends", even though from the perspective of people alive today these outcomes are very similar.

I think relative to neartermist intuitions about catastrophic risk, the particular focus on extinction increases the threat from AI and engineered biorisks relative to e.g. climate change and natural pandemics. Basically, total extinction is quite a high bar, and most easily reached by things deliberately attempting to reach it, relative to natural disasters which don't tend to counter-adapt when some survive.

Longtermism also supports research into civilisational resilience measures, like bunkers, or research into how or whether civilisation could survive and rebuild after a catastrophe.

Longtermism also lowers the probability bar that an extinction risk has to reach before being worth taking seriously. I think this used to be a bigger part of the reason why people worked on x-risk when typical risk estimates were lower; over time, as risk estimates increased. longtermism became less necessary to justify working on them.

One takeaway, I think, is that these things which already seem good under common sense are much more important in the longtermist view.  For example, I think a longtermist would want extinction risk to be much lower than what you'd want from a commonsense view.