Would you trade for Ken Griffey, Jr. even though he's not an upgrade for your team at any position? It could be worthwhile: he'd provide good depth, regular rest for your OF/DH types, and a very good pinch-hitting option for the late innings.
How about trading for him and starting him every day in center field, weakening both your hitting and your defense? That's where I draw the line.
I pick on Kenny Williams a lot, maybe more than he deserves. His trade for Carlos Quentin is the biggest reason the Sox are still in the race, and John Danks has been a key part of this year's surprise team as well. However, moves like the Griffey trade threaten to undo all his good work.
Tonight Griffey is starting in center field, even though the Sox are facing a lefty. Nick Swisher--switch-hitter, a better bat than Griffey and a better fielder--is riding the pine so the Sox can show off their shiny new acquisition. So far, Griffey has repaid the Sox with two strikeouts in his two at-bats, plus he's misplayed two singles to center field into a double and triple--all in four-and-a-half innings.
Still, it's clear that the trade satisfied Chicago's most important need: Williams's man-crush on Griffey. I imagine Williams is the type of guy who goes to his high school reunion to bang an ex-cheerleader, even though she's put on a hundred pounds and has the personality of toothpaste. After all, she was so hot ten years ago.
To the Sox's credit, Griffey is more famous than Swisher AND higher-paid, two traits that are much more desirable in an everyday center fielder than the abilities to hit and field.