Well, you know, either windows or Mac, includes a complex permission management system. I think providing this feature could help solving many unknown and hard to pinpoint permission issues generated by whatever user or applications. Just like kwokkaron says, we use this to solve problems in a single click.Because it happens automatically now and also "rootless" prevents apps from changing system files and their permissions.
On a side note, I find it quite amusing how people have fallen in love with "repair permissions" over the years and think it makes any significant difference to how OS X runs.