But if there is no Google/Apple button, will you just leave? Like not even create an account? That's what "conversion killer" means.

I may start to create an account, but after about 30 seconds of effort, I'll start asking myself if it's really a service I care about. Send me an email? If it's not there by the time I click my email tab, odds are pretty good I won't wait around unless it's a truly compelling offering. Want me to fill out a form? If it's anything more than just an email and a password field my password manager can complete for, again, I'll question whether I want you to have that info about me.

So no, I may not leave, but each tiny bit of friction increases the possibility of abandonment. From the perspective of conversion, abandonment is the same as "just leaving".

I won't but a decent % of people do ye.

In fact a decent % of people stops shopping on your site if there's a few ms lag.

At every step a few percent of revenue is lost your competitor takes in.