IME freelances and contractors use it a fair bit, permies may maintain a profile just in case, but mostly update it when they're changing jobs. Not having a profile doesn't harm you but it also doesn't help- because it's so easy to look people up the system of contacts, endorsements and recommendations is useful to establish an element of credibility. Chancers who claims widespread experience with a well maintained but thin profile get found out pretty quickly, because every workplace has a few social media tarts who will pair with anyone and everyone the moment they walk through the door.
So if you're going to do it, invest some time. Think through what you can honestly say about each past job/experience, remember some friendly names, look them up and ask to pair with them, the system will then suggest more. Don't over-stuff your contacts with irrelevant mates, it's not facebook, and don't endorse those miles above your paygrade for stuff you know nothing about, they'll think you're an idiot.