When I play USTA Mixed Dubs, it's all out, all the time. To me (and my female partner) it's two people on the other side trying to beat us. No distinction between the two sexes. My last match had smashes going in equal numbers to both their feet. This same match, the opposing guy had a really good serve, and he didn't back off at all when serving to my partner. Granted, she's got a huge forehand, but I would never expect him to tone it down.
I have played where I was just randomly filling in the fourth spot with 3 little old ladies playing 3.0 doubles. In that situation, I made sure I never won any points. I would topspin lob with them back and forth, nice slow volleys etc. No smashes. When you know you can win any point at will, why go for it?