The QO doesn't serve some players as much as others though.  The problem with the QO is that unlike things like the MLE, the QO is based on the previous salary.  If you were a high pick, the QO is accordingly high.  If you were a later first rounder or second rounder, it may not be much above the NBA minimum.   There's no reward for outperforming your draft position.  Taking the one year deal accordingly brings a different level of risk vs. injury or other change in perceived value.  It was a better deal for Pietrus than for Varejao even though the latter is a much better player.

Varejao's QO was 1.2 million.  Waiting a year means diluting whatever next contract he has by virtue of a year at that price if he was playing the strategy of "I'll take the low salary now for a bigger payday."  Let's assume on the open market he could get a Darko deal averaging about $7mil per.  The bigger payday would be bigger potentially, but essentially divided over one more season.  Waiting a year on a big contract could effectively mean the difference between a 5 year/35 million really being a 6 year 36.2 million.  That's a million a year over the life of the contract.