I think this is true as a hiring manager, but isn't necessarily true for an interviewer, who may be a senior engineer applying a very strong filter to the "who would I want on my team" test.

Uh, unless you saw a better candidate earlier in the day/week.

I'm senior enough that if I rate two people strong hire, I'm capable of getting more budget. This has in fact happened recently -- we couldn't decide between two great candidates, so we offered and hired both.

That depends on the size of the company, no?

Yes, and in some cases, the company needs one person now, and another one a bit later. Then can be nice to have a list of people who did well, to contact again

Same. If someone makes it that far, I (and several others) have already decided that they stand out. So I'm secretly rooting for them the moment the interview starts.