What are the benefits of setting electrical switches at the center of drywall seams?
It's easier to cut the drywall when the bottom of the switchbox is sticking out from the bottom of the top drywall panel.  Drywallers cut receptacle box holes with the drywall in place using a rotary tool.  It's easier to cut the hole when the panel doesn't cover the whole box.  There's not any impact to mudding, because, like you noted, you have to fill the joint flat either way.