This answer is directed at instant runoff voting vis-a-vis multiple round voting, such as systems where a majority of the vote is required to win the final round.
The big virtue of multiple round voting is that it is easier for many voters, in terms of both time expended for candidate research, and conceptual difficulty, to make a first choice pick only, than it is to rank other contenders in a race beyond the first choice candidate.
In a multiple round voting system, if your first choice candidate doesn't win in the first round, you have additional time to research the candidates who remain, knowing that the research is directly relevant to the outcome, without having to have spent a lot of useless time researching second and third priorities in races where it will never come to an "instant runoff" because first choice decisions will end up resolving the race, or where a voter's first choice makes it into the next round.
Thus, the decision on second choice candidates in a second round is likely to be better informed and hence higher in quality, than in an instant runoff voting conceptual "second round".
The downside of having multiple rounds is that often this is framed as a "top two candidates in the first round" make the second round, and when this happens, the candidates who make it into the second round may not accurately reflect the second choices of the voters whose first choice candidates are eliminated.