LinkedIn will soon celebrate its 14th birthday. It now has roughly half a billion users, a quarter of whom are in the United States. Every second, two more professionals join LinkedIn. So what’s up with all these people suddenly endorsing your skills?

I’m not talking about the “Recommendations.” LinkedIn has had that feature since the early days and it’s rarely used, except when someone’s looking for a job and asks someone else to write a recommendation for them.

No, I’m talking about the “Skills Endorsements” added more recently. It seems as if every day someone new is endorsing me (and probably you). I think this feature is a great addition to LinkedIn although many users are still confused by it.

Here’s why it’s important: When somebody signs up for LinkedIn they’re asked to list their skills. You may not remember doing this yourself because it was a day-one activity, not repeated thereafter. The problem with the collective lists of our skills is that they’re all self-reported. In a world where resume padding is legendary (remember the CEO who Yahoo quickly hired and then fired?), how valuable is a self-reported list?

Whenever someone views your profile LinkedIn poses a question: “Does [your name here] have these skills or expertise?” LinkedIn then presents five randomly selected skills from among those you claimed, offering the viewer the opportunity to “endorse” or “skip” any or all.

Think about it. A given associate may not have a full view of your skills, but when everybody weighs in that’s likely to be on target.

What am I more likely to believe about you, the skills that you claim or what everyone else says?

See how this makes LinkedIn’s personnel data more valuable?

Addressing one other mystery, I’ve frequently heard people say, “There’s no way that Jane Smith would have viewed my profile.” Indeed, she may not have but if she viewed and endorsed someone else’s profile LinkedIn then displayed four of her connections listing one skill for each and asked “What skills or expertise do your other connections have?”

So be careful who you link with. Hint: Stick to people you know and respect professionally. That’s what LinkedIn advises.

You might want to review your own profile. What does the world say about you? For that matter, what does the world say about your potential customer or potential employee?

That could be even more valuable to know.