The value chart is used for draft picks not players that are involved. Once you get into players things get complicated, thats why you rarely see players included with picks in draft day deals, because there is no value chart
they absolutely do sit there with a value chart
it serves as the starting point to every deal, you add up and find what makes the deal even on all sides, then the desperate team may add more to sweeten the deal and get it done. Where do you think trades start from? A team that wants to move up or down looks at what they have to give up or gain in return. I've seen GM after GM talk religiously about the value chart, i dont know what draft you've been following the past 10 years.