The Grandy Man hit .232/.319/.492 with 43 homers in 160 games as the Bombers center fielder in 2012 and has hit .247/.337/.506 in his three seasons in pinstripes. So it's clear that he's been very productive, in fact, he's been one of the most productive hitter on the team during this span. The 31 year old has one year left on his contract worth $15 million so many fans have given this and his increasing strikeout rate as reasons to get rid of him.
Now, he did strikeout a career high 28.5% of the time in 2012, which is definitely a ton, but when it comes with the type of power that he produces at a premium position, it makes it worth it. Add in the fact that the offense is losing 40+ homers between Martin and Swisher and the Yankees need all of the power they can get. You can say that losing the power is a good thing because the team 'hits too many homers,' but that's just silly. That doesn't exist.
The point here is that the Yanks are still trying to field a winning team and I don't know how they would replace Granderson if he was shipped out. Also, they would probably be getting zero power from all three outfield positions, which does not bode well for a team that hopes to compete. So even though the strikeouts do get frustrating, the power that comes with it is very valuable and is something that's going to help this team a lot in the coming year.