Technically, restrictions on employees by their FORMER employer. In theory (if valid), they could retain power over you for a time AFTER you are no longer employed.
A similar thing is often done during dismissal: sign away your rights to sue for wrongful dismissal in return for severance. In my case, almost a year's worth of pay seemed like a reasonable severance, so I took it and didn't argue.
Not really. Individuals who can build a company are under no obligation to sell it to anyone placing unreasonable conditions on the sale. If I'm buying your company, I have a concern that you might pull of of the customers back (having started a new company) but the price I'm willing to offer you compensates you for the book of business you are selling to me. That's where non-solicitation clauses come in.
I think the operative principal here is that employees are at a disadvantage w/r to employers. Buyers and sellers are not presumed to be at any disadvantage w/r to each other.
A similar thing is often done during dismissal: sign away your rights to sue for wrongful dismissal in return for severance. In my case, almost a year's worth of pay seemed like a reasonable severance, so I took it and didn't argue.