But it's not evidence of anything other than than a company has valued that potential employee at a particular rate. What an employee is worth to an employer is pretty subjective. Someone that is worth 7 figures to one company may only be worth 6 or 5 to another.

Having an offer in hand is valuable to the employee, certainly! There's nothing wrong with getting an offer, then asking your current employer for a raise that would meet or exceed that offer. The issue I have is actually communicating that offer to the current employer.

Now, don't get me wrong -- I'd certainly never punish or fire anyone who did that. I'm just not going to give in to what I perceive as extortion, and what I perceive as being unfair to the employer who made the offer.