You often see them in the context of a sale of business, where the buyer requires the seller not to compete with him for a specified period. They are also frequently found in employment agreements, especially where senior staff are involved, in which case they prevent the employee from undermining the employer’s business for a specified period after the employment comes to an end. 

That is a natural consequence of putting two groups of people together with different needs and expectations, in an occasionally stressful environment.