I've had a few of these. Honestly, they're pretty hard to actually trigger. At least in mine, short of something along the lines of corporate espionage or insider trading, there's not much in there that's vague enough to hinder career prospects since, I assume, they're legally not allowed to. It's generally been, "You can't work for another company on this very specific thing you never heard of before starting here and will probably never hear of again, for the next 24 months."

Haven't heard of them being misused for retention out in the wild, but I assume they must be enough to cause this.