Realistically, it's a tribal signal to cargo culting manager types who like to talk about percentages and like pointing to flipcharts with a stick in a suit.
It doesn't matter what number you put there.
If you're writing to numerate, technical types don't do this, because technical people know that just a percentage without context makes no sense. You reduced costs by 16%? Costs of what? What's the denominator? You increased engagement? What does that mean? Subscribers? Clicks? Time spent?
This is the same kind of thing as when academics sprinkle unnecessarily complicated-looking math equations to describe plainly obvious things with impressive symbols, when it's objectively unnecessary. The goal is to give it a certain look, to signal seriousness.
As silly as it may sound, it probably actually works.
Since we are on HN, probably many of you know the Paul Graham classic "Submarine" [1] post,
> Our greatest PR coup was a two-part one. We estimated, based on some fairly informal math, that there were about 5000 stores on the Web. We got one paper to print this number, which seemed neutral enough. But once this "fact" was out there in print, we could quote it to other publications, and claim that with 1000 users we had 20% of the online store market.
> This was roughly true. We really did have the biggest share of the online store market, and 5000 was our best guess at its size. But the way the story appeared in the press sounded a lot more definite.
> Reporters like definitive statements. For example, many of the stories about Jeremy Jaynes's conviction say that he was one of the 10 worst spammers. This "fact" originated in Spamhaus's ROKSO list, which I think even Spamhaus would admit is a rough guess at the top spammers. The first stories about Jaynes cited this source, but now it's simply repeated as if it were part of the indictment. [4]
> All you can say with certainty about Jaynes is that he was a fairly big spammer. But reporters don't want to print vague stuff like "fairly big." They want statements with punch, like "top ten." And PR firms give them what they want. Wearing suits, we're told, will make us 3.6 percent more productive.
I think it's similar with certain hiring managers too. They want definite statements, because it provides for CYA ammo. The guy looked great on paper, look at those percentages!