Small nitpick: in most cases, these companies make a hiring decision with just one round of interviews (if you exclude the technical phone screen, which is a way to reduce wasting everyone's time when it's obvious it's a poor fit).

As both a candidate and as a hiring manager, I much prefer to have a single round of on-site interviews, vs. having the candidate come on site more than once. Good candidates probably have a good job already, and asking them to take multiple half days off to interview is an unnecessary burden.