An example is custom hardware not working as expected. To debug this you may need five different people on the line at the same time. If you do this in an async manner it will take days or weeks to resolve.

But can be resolved...

Pair programming!

This is the only one that actually is valid. Good point!

1:1 career conversations

You can't have these in slack async? (because I have)

I don't believe you can have that conversation effectively if each person gets to send one message per day due to timezone-induced lack of workday overlap.

Day 1 M> So, what do you think your next career move would be?

Day 2 E> I don't know. I really enjoy software engineering, but I think I'm ready to take on some kind of leadership role.

Day 2 M> OK, that's great. Do you need any kind of support before taking that on?

Day 3 E> I'm not sure what you mean.

Day 3 M> ...

It can work if you're not in a rush. If you need to wait overnight to get help with something that slows you down.

So its a trade off? But still can't name one..