I think neither. They buy back when they have the cash to buy back with! That's smart because it increases the value of their stock, which leads to others also buying more of it. Since they are paid bonuses in stock, using company money to increase the value of what they are being paid is smart. Nefarious, but smart.
RE: Goldman Sachs Warns U.S. Stock Market SCREAMING Overvalued! Way Overdue For Crash!