Our place is ventilated well enough that I don't need to open the windows for ventilation or to manage humidity per se, but I am fortunate enough to live in an area with good quality air, so I often do in spring/summer/fall just because it feels fresher.

In winter, I don't want to freeze or waste energy, so I usually keep them closed. But once in a while, if I have my computer running for a long time and the heat is also on for the rest of our place, I may crack the window a bit just to keep that room from becoming unbearably hot.