See, the only one who really know how significant the strikes are, is the guy receiving them- so judges have to look for visible signs of significance, eg: knock backs or knockdowns. So, for example, when they saw Diaz fall down a couple times in the first round, they gave the round to McGregor. But as a fighter who's spent a significant amount of time striking, I can see that those knockdowns didn't actually damage Diaz much- in fact, from my perspective, the most damaging blows in the fight happened while both fighters remained standing. But as a judge, I have to see it this way: knockdown > knock-back > landing a strike. And that's kind of unfair in a lot of situations because a strike that pushes doesn't do nearly as much damage as a strike that penetrates. Similarly, strikes that visibly cut or otherwise leave visible damage will generally score higher than strikes that don't- and that's also kind of dumb sometimes because then it becomes a random contest of who has more malleable skin or who bleeds more easily. A scary looking facial laceration caused by friction from a glove skidding across the skin isn't nearly as dangerous as a concussive blow that rattles the brain- but since judges don't have X-ray vision, they have to go on what they can see.
Judging is based on effective striking, effective grappling, and effective aggressiveness- in that order. But some organizations tally up the scores differently. ONE FC, for example, the judges are required to record, catalog, and score basically every single combative movement of the fight (which is problematic IMO when fighters start throwing blind reckless busy flurries that score high but don't actually cause damage), whereas a lot of other fight shows, judges are looking only for the big stuff. I'm not sure how nit-picky the UFC is about judging every strike thrown right now, because they record everything and report post fight, but it's often been the case that the fighter who scored more "significant strikes" according to the fight metrics loses the decision according to the judges.
And oh man, the term "significant strikes" is a joke, since any time a limb touches another fighter it can be considered a "significant strike". If it was truly that significant, no mortal man could take 200 of them in a single match.
All that being said, I would have loved to see another couple minutes on the clock in the last round to see what Diaz would have done on the ground, and it kind of made me wish that UFC would switch to a one long round format, but meh, it's a sport with an artificially imposed round system imposed by boxing commissions because of traditions from a bygone era with judging parameters that have drastically changed over and over in the last 20 years because reasons, so what are you going to do?