Just because they are non-enforceable doesn't mean they have no effect. The COO of one of past employers was offered a job at a competitor shortly after he was fired. When the new company heard of his non-compete clause and the intent of the old company to enforce it, they withdrew their offer.
(It's also the case that one of our large competitor firms, at least at the time, put non-competes in place that effectively wouldn't let anyone who left work for any competitor. i.e. they couldn't do the same job at any other firm. And, apparently, they enforced these agreements rather vigorously.)