I play much more offensively and aggressively in doubles than in singles. In singles I try to play percentage tennis and look for openings or short balls to attack, however, even in those situations I usually try to set up a winner rather than hit it outright at the first opportunity. The only thing I do more offensively in singles is serve where I try to hit bigger serves to take control of the point. On the other hand, in doubles I will try to take something off my first serve to get a higher percentage of them in, particularly when I have a good net player as a partner.
In doubles though I try to be the fly in the ointment so to speak and disrupt anything coming across the middle. Even if I sometimes get burned down the line I see that as just a cost of doing business and controlling the middle. I serve and volley on 100% of first serves and a high percentage of second serves until the receivers prove to me that they are capable of winning more than 50% of those points.
When should you serve and volley in doubles? Only when you want to win.