I was once so asked to sign one. It was shuffled between the NDA and the "at will appointment"  agreement. It was ridiculously broad. And basically said once I leave I can't do any welding or fabrication work for 2 years.

I refused to sign it. Still got the job. 

At another point My career I did sign one. But it was so specific to the company's hyperfocused niche It really didn't seem to be an issue. 

The thought of bureaucrats having the authority to ban a certain type of contract gives me indigestion.